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

In vivo measurement of nitric oxide production in porcine gut, liver and muscle during hyperdynamic endotoxaemia

1. During prolonged endotoxaemia, an increase in arginine catabolism may result in limiting substrate availability for nitric oxide (NO) production. These effects were quantitated in a chronically instrumented porcine endotoxaemia model. 2. Ten days prior to the beginning of the experiments, pigs were catheterized. On day 0, pigs received a continuous infusion of endotoxin (3 microg kg(-1) h(-1)) over 24 h and were saline resuscitated. Blood was drawn from the catheters at 0 and 24 h during primed-infusion of (15)N(2)-arginine and P-aminohippurate to assess (15)N(2)-arginine to (15)N-citrulline conversion and plasma flow rates, respectively, across the portal-drained viscera, liver and hindquarter. 3. During endotoxin infusion a hyperdynamic circulation with elevated heart rate, cardiac index and decreased mean arterial pressure was achieved, characteristic of the human septic condition. 4. Endotoxin induced NO production by the portal-drained viscera and the liver. The increased NO production was quantitatively matched by an increase in arginine disposal. Nitrite/nitrate levels remained unchanged during endotoxaemia. 5. Despite an increased arginine production from the hindquarter and an increased whole-body arginine appearance rate during endotoxin infusion, the plasma arginine concentration was lower in endotoxin-treated animals than in controls. 6 On a whole-body level, the muscle was found to serve as a major arginine supplier and, considering the lowered arginine plasma levels, seems critical in providing arginine as precursor for NO synthesis in the splanchnic region.

Nitric oxide scavenging, alone or with nitric oxide synthesis inhibition, modulates vascular hyporeactivity in rats with intraperitoneal sepsis

Elevated levels of nitric oxide (NO) may be a primary cause of the vascular hyporeactivity (vasoplesia) and refractory hypotension in sepsis. This study was initiated to determine the efficacy of NO scavenging with acellular hemoglobin (Hb) solution in modulating sepsis-mediated vasoplesia. Male Sprague Dawley rats were subjected to sepsis by cecal ligation and puncture (CLP). Twenty-four hours post-CLP, the animals were randomly assigned to one of four groups (n = 5-6 each) and given an intravenous injection of 0.5 mL bovine serum albumin (BSA; 5 g/dL), 0.5 mL human Hb (7g/dL), 50 microL Nomega-nitro L-arginine methyl ester (NAME; 1 M), or both Hb and NAME. Blood pressure (BP), cardiac output, systemic vascular resistance, and vascular reactivity (VR) to norepinephrine (NE; 40 ng/Kg) were assessed before and after an experimental treatment. In some animals, inducible NO synthase (iNOS) mRNA expression was assessed in selected tissue samples harvested at the conclusion of experiment using a reverse transcription-polymerase chain reaction (RT-PCR) method. Treatment with Hb, NAME, or NAME + Hb elicited a significant improvement in mean BP and VR compared with the control (BSA) group (P < 0.05, analysis of variance and Neuman-Keuls tests). Tissue samples from 24-h CLP rats clearly exhibited iNOS gene expression; higher iNOS gene expression in the intestine compared with aorta suggests that the intestine may be a major source of the elevated NO level in this model. In conclusion, NO scavenging with Hb, alone, or in combination with NO synthesis inhibition, appears to be effective in modulating sepsis-mediated vascular hyporeactivity and may reduce complications associated with global NO synthesis inhibition.

Lipopolysaccharide-induced enterocyte-derived nitric oxide induces intestinal monolayer permeability in an autocrine fashion

Studies indicate that endotoxin (LPS) causes intestinal injury, increases inducible nitric oxide synthase (iNOS) activity, leads to increased NO production, and promotes bacterial translocation (BT). To investigate the mechanism by which LPS causes gut injury and to test the hypothesis that NO produced by enterocytes promotes gut injury in an autocrine fashion, rat intestinal epithelial cell (IEC-6) monolayers were tested. IEC-6 monolayers grown in a bicameral system were incubated with media or with LPS (25 microg/mL) and tested for permeability to phenol red, BT, and nitrate/nitrite (NO2/NO3) production. To determine the direct effect of NO on permeability, monolayers were incubated with the NO donor S-nitroso-acetylpenicillinamide (SNAP; 1 mM) and tested for permeability. Next, the protective effects of two NOS inhibitors (L-NMMA and L-NIL) were tested. Finally, to determine if LPS-induced permeability occurs via a poly (ADP-ribose) synthetase- (PARS) dependent pathway, monolayers incubated with LPS alone or with the PARS inhibitor, INH2BP (100 microM) were tested. LPS significantly increased IEC-6 permeability to phenol red, as well as increased NO2/NO3 by 20-fold (P < 0.001) and increased BT 10-fold (P < 0.001). SNAP mimicked the effect of LPS and significantly increased both permeability to phenol red and BT. Inhibition of iNOS significantly decreased the LPS-induced increase in monolayer permeability and BT (P < 0.05). Monolayers incubated with INH2BP had significantly decreased permeability to phenol red and BT, suggesting that LPS-induced NO production increases monolayer permeability at least in part via a PARS-dependent mechanism. In summary, LPS-induced disruption of monolayer barrier function appears to be related, at least in part, to enterocyte produced NO. This supports the hypothesis that NO produced by LPS-stimulated enterocytes promotes injury in an autocrine fashion and highlights the fact that enterocytes can be a target as well as a producer of NO.

The gastrointestinal tract in critical illness

The gut has often been suggested to be one of the essential factors in the pathogenesis of many nosocomial infections and possibly multi-organ failure. In the light of several recent studies, the importance of normal gut bacterial flora and the role of the gastrointestinal tract in human immune function are now better understood. It now seems clear that stimulation of gut-associated lymphoid tissue through enteral feeding is the key to the preservation of mucosal-derived immunity; however, the role of this native gastrointestinal immune function in the subsequent development of sepsis and multi-organ dysfunction syndrome remains the subject of ongoing study.

Molecular cloning and characterization of a metal responsive Chironomus tentans alpha-tubulin cDNA

Metal pollution of aquatic ecosystems is a problem of economic and health importance. Sensitive molecular biomarkers of metal exposure are sorely needed. We have isolated a cDNA from the midge Chironomus tentans that is transcribed in all organs and developmental stages. The cDNA encodes a protein, designated Chironomus tentans alpha-tubulin 1 (CTTUB1), which has significant similarities with invertebrate and vertebrate alpha-tubulins. CTTUB1 is abundantly transcribed in embryos and to a lesser extent in adults and larvae. CTTUB1 RNA and protein abundances are increased in larvae exposed to copper or cadmium. The pattern of cellular distribution of CTTUB1 protein in the midgut epithelial cells was radically affected by cadmium. In the midgut cells of unexposed larvae, CTTUB1 was found evenly distributed throughout the cytoplasm, while in cadmium-exposed larvae, CTTUB1 was mostly concentrated along the basolateral plasma membrane. A mechanism for the regulation of alpha-tubulin synthesis by cadmium is proposed. This is the first report on the isolation of a metal responsive gene from a neartic aquatic insect.

Developmental variability in expression and regulation of inducible nitric oxide synthase in rat intestine

Inducible nitric oxide synthase (iNOS) may be a key mediator of intestinal injury, which varies with developmental age. One member of the mitogen-activated protein kinase (MAPK) family, p38, is involved in the lipopolysaccharide (LPS)-mediated iNOS induction. The involvement of p38 MAPK in basal and LPS-induced iNOS expression was examined in the rat intestine at two developmental ages. Neonatal (4 days postnatal) and adolescent (15 days postnatal) rats were injected with LPS (5 microg/g ip), a selective p38 inhibitor (SB 203580), or both. Tissue was removed after 4 h and 6 h for mRNA and protein analysis. iNOS mRNA and protein were markedly upregulated in the adolescent female following LPS exposure, whereas males had an attenuated response. Neonates had a minimal response. SB 203580 suppressed LPS-induced iNOS mRNA and protein in the ileum, more so in females than in males. Adolescent ileal p38 activation was constitutively high and nonresponsive to LPS. Basal and post-LPS p38 phosphorylation was low in neonatal ileum. We conclude that ileal iNOS expression is developmentally regulated and influenced by gender and that p38 is permissive for LPS effect. The developmental regulation of p38 may contribute to age-dependent variations of intestinal injury.

Inducible nitric oxide synthase gene knockout mice have increased resistance to gut injury and bacterial translocation after an intestinal ischemia-reperfusion injury

OBJECTIVE

Intestinal ischemia-reperfusion after severe shock states is often associated with bacterial translocation and intestinal barrier dysfunction. Our previous studies showed that inducible nitric oxide synthase (iNOS) gene knockout mice were resistant to endotoxin-induced bacterial translocation and ileal mucosal damage. The goal of this study was to test whether iNOS mediates bacterial translocation after intestinal ischemia-reperfusion, using iNOS knockout mice (iNOS-/-) and their wild-type littermates (iNOS+/+).

DESIGN

Prospective animal study with concurrent controls.

SETTING

Small animal laboratory.

SUBJECTS

Thirty-eight iNOS knockout mice and 51 wild-type littermates.

INTERVENTIONS

iNOS+/+ mice or iNOS-/- mice were subjected to a sham operation or 30 mins of superior mesenteric artery occlusion followed by reperfusion. Twenty-four hours after reperfusion, bacterial translocation to mesenteric lymph nodes, ileal villous damage, and cecal bacterial population were evaluated.

MEASUREMENTS AND MAIN RESULTS

Sham operation did not induce bacterial translocation, change cecal bacterial population levels, or cause ileal villous damage. Intestinal ischemia-reperfusion caused bacterial translocation in 72% of the iNOS+/+ mice but only 28% of the iNOS-/- mice. Both iNOS+/+ and iNOS-/- mice subjected to superior mesenteric artery occlusion (SMAO) in which bacterial translocation occurred had cecal bacterial population levels that were three logs higher than mice subjected to sham SMAO or mice subjected to SMAO in which bacterial translocation did not occur. The magnitude of villous injury was less in the iNOS-/- mice than the iNOS+/+ mice after SMAO, although the incidence of ileal villous damage was significantly higher in both the iNOS+/+ and iNOS-/- mice in which bacterial translocation occurred after SMAO than in the mice in which bacterial translocation did not occur after SMAO. iNOS+/+ mice subjected to SMAO had increased plasma concentrations of nitrite (NO2-) and nitrate (NO3-), and the plasma concentrations of NO2- and NO3- were highest in the mice in which bacterial translocation had occurred.

CONCLUSION

iNOS knockout mice were more resistant to intestinal ischemia-reperfusion-induced bacterial translocation and mucosal injury than wild-type mice, suggesting that iNOS might play a role in intestinal ischemia-reperfusion-induced loss of gut barrier function.

Endotoxin-induced ileal mucosal injury and nitric oxide dysregulation are temporally dissociated

Despite recent investigations, the mechanisms responsible for intestinal epithelial injury during endotoxemia remain unclear. The present study tests the hypothesis that epithelial necrosis and/or apoptosis correlate with nitric oxide (NO) dysregulation in a nonischemic model of sepsis-induced ileal injury. To test this hypothesis, a well-established in situ, autoperfused, feline ileal preparation was employed. After endotoxin (lipopolysaccharide [LPS], 3 mg/ kg, intravenously; n = 9) or vehicle (control; n = 5) treatment, ileal segments were obtained at baseline, 2 and 4 h for simultaneous evaluations of cellular and mitochondrial ultrastructure, immunoprevalence of inducible nitric oxide synthase (iNOS) and 3-nitrotyrosine (a stable biomarker of peroxynitrite), and histochemical evidence of apoptosis. Epithelial necrosis was prominent by 2 h post-LPS, despite unaltered global ileal tissue oxygen content, blood volume, and blood flow. Significant evidence of apoptosis and increases in the immunoprevalence of iNOS and 3-nitrotyrosine were not evident until 4 h post-LPS. These results suggest that the early ileal mucosal necrosis may be due to LPS-induced activation of inflammatory pathways and/or microcirculatory disturbances, whereas NO dysregulation may participate in later events, including protein nitration and epithelial apoptosis.

Hypoxic signal transduction in critical illness

Derangements in tissue perfusion occur during critical illness, and the resulting deficit in oxygen delivery may play an important role in the pathogenesis of hemorrhagic and septic shock. Cells and organisms have developed a variety of adaptive strategies to maintain adequate energy production to maintain normal cellular function under hypoxic conditions. Recent studies from our laboratory suggest that certain proinflammatory cytokines, which are likely to be elaborated during or after shock, can interfere with the ability of cells to adapt to hypoxia, and thereby contribute to the development of organ system dysfunction.

Ileal mucosal oxygen consumption is decreased in endotoxemic rats but is restored toward normal by treatment with aminoguanidine

OBJECTIVE

We sought to test the hypothesis that ileal mucosal oxygen consumption is impaired in endotoxemic rats.

METHODS

Male Sprague-Dawley rats were injected intravenously with either Escherichia coli lipopolysaccharide (5 mg/kg) or a similar volume of vehicle. A segment of ileum was excised 8 hrs later, and the serosal and muscular layers of the bowel were stripped away from the mucosa. A strip of mucosa was mounted in a polarographic chamber containing air-saturated Krebs-Henseleit buffer plus 20 mM glucose, PO2 being monitored during a 10-min period. Some rats were injected intraperitoneally with the inducible nitric oxide synthase inhibitor, aminoguanidine (30 mg/kg per dose), or a similar volume of vehicle, at 1, 3 and 6 hrs after injection of lipopolysaccharide.

RESULTS

In an initial experiment, the rate of oxygen consumption was significantly lower for mucosal samples from endotoxemic rats as compared with control rats (0.76+/-0.11 ng-atoms vs. 1.42+/-0.22 ng-atoms of 0/min per microg dry weight, respectively; n = 8 per group; p<.05). The rate of mucosal oxygen consumption was higher in aminoguanidine-treated as compared with vehicle-treated endotoxemic rats (1.25+/-0.11 ng-atoms and 0.73+/-0.07 ng-atoms of 0/min per microg, respectively; n = 7 and n = 6, respectively; p<.05).

CONCLUSION

Endotoxemia is associated with diminished intestinal mucosal oxygen utilization due to an intrinsic acquired derangement in cellular respiration that is caused, at least in part, by an aminoguanidine-inhibitable mechanism.

Regulation of induction of nitric oxide synthase and the inhibitory actions of dexamethasone in the human intestinal epithelial cell line, Caco-2: influence of cell differentiation

1. The inducible isoform of nitric oxide synthase (iNOS) may be involved in the pathogenesis of inflammatory bowel disease. Using the human intestinal epithelial cell line, Caco-2, iNOS expression, regulation and sensitivity to the glucocorticoid, dexamethasone after cytokine exposure and its relationship to the degree of differentiation has been studied. 2. NOS activity, assessed by NO2- and NO3- release, was time-dependently increased after exposure to interferon gamma alone or in combination with interleukin-1beta and tumour necrosis factor alpha. 3. Cytokine-induced iNOS activity was increased with days in culture over 20 days and number of passages, suggesting iNOS up-regulation during enterocyte-like differentiation. This activity was inhibited by the selective iNOS inhibitor 1400 W (0.1 - 100 microM). In addition, iNOS protein induction was confirmed by Western blot. 4. Actinomycin D (5 microg ml(-1) inhibited cytokine-induced iNOS activity, protein expression and mRNA level. Pyrrolidine dithiocarbamate (PDTC: 10 - 200 microM) and 3,4 dichloroisocoumarin (0.1 - 100 microM) reduced cytokine-induced iNOS activity and protein expression at both day 10 and 15 after confluence. PDTC also decreased iNOS mRNA levels, suggesting NF-kappaB involvement in its transcription at these times. 5. The tyrphostins A25 and B42 reduced cytokine-induced iNOS activity at both day 10 and 15 after confluence, indicating the JAK-2 kinase is also involved at these times. The tyrphostins also reduced the iNOS protein expression. 6. Dexamethasone (0.1 - 10 microM, for 24 h) reduced cytokine-induced iNOS activity at day 15 and 20 after cell confluence, but not at day 5 or 10. 7. Dexamethasone (5 microM) decreased cytokine-induced iNOS protein expression at day 10 as well as at day 15 after confluence. 8. These findings indicate that iNOS induction and its inhibition by dexamethasone in this human intestinal epithelial cell line is dependent on the degree of differentiation.