Biology of nitric oxide signaling

Activation of poly(ADP-Ribose) polymerase-1 is a central mechanism of lipopolysaccharide-induced acute lung inflammation

Recent studies demonstrated that activation of the nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP-1) by oxidant-mediated DNA damage is an important pathway of tissue injury in conditions associated with oxidative stress. Using a dual approach of PARP-1 suppression, by genetic deletion or pharmacological inhibition with the phenanthridinone PARP inhibitor PJ-34, we now demonstrate an essential role of PARP-1 in the development of pulmonary inflammation induced by lipopolysaccharide (LPS). PARP-1+/+ and PARP-1-/- mice received an intratracheal instillation of LPS (50 microg), followed after 24 h by bronchoalveolar lavage to measure the cytokines TNF-alpha, IL-1beta, and IL-6, the chemokines MIP-1alpha and MIP-2, leukocyte counts and myeloperoxidase activity (neutrophil accumulation), protein content (high permeability edema), and nitrite/ nitrate (nitric oxide production). Malondialdehyde (an index of lipid peroxidation) was measured in lung tissue. Similar experiments were conducted in BALB/c mice treated with PJ-34 or vehicle. The absence of functional PARP-1 reduced LPS-induced increases of cytokines and chemokines, alveolar neutrophil accumulation, lung hyperpermeability, NO production, and lipid peroxidation. Histological analysis revealed attenuated lung damage after PARP inhibition. Our findings support a mechanistic role of PARP-1 in the regulation of LPS-induced lung inflammation. Pharmacological inhibition of PARP may be useful in clinical conditions associated with overwhelming lung inflammation.

Dietary glycine inhibits activation of nuclear factor kappa B and prevents liver injury in hemorrhagic shock in the rat

We investigated the effects of a glycine-containing diet (5%) on liver injury caused by hemorrhagic shock and resuscitation in rats. Anesthetized rats were bled to a mean arterial blood pressure of 35-40 mm Hg for 1 h and then resuscitated with 60% of shed blood and lactated Ringer's solution. Feeding the rats glycine significantly reduced mortality, the elevation of plasma transaminase levels and hepatic necrosis. The increase in plasma TNFalpha and nitric oxide (NO) was also blunted by glycine feeding. Hemorrhagic shock resulted in oxidative stress (significant elevations in TBARS and in the oxidized/reduced glutathione ratio) and was accompanied by a reduced activity of the antioxidant enzymes Mn- and Cu,Zn-superoxide dismutase, glutathione peroxidase and catalase, overexpression of inducible NO synthase (iNOS), and activation of nuclear factor kappa B (NF-kappaB). Glycine ameliorated oxidative stress and the impairment in antioxidant enzyme activities, inhibited NF-kappaB activation, and prevented expression of iNOS. Dietary glycine blocks activation of different mediators involved in the pathophysiology of liver injury after shock.

Infusion of methylene blue in human septic shock: a pilot, randomized, controlled study

OBJECTIVE

To evaluate the effects of continuous infusion of methylene blue (MB), an inhibitor of the nitric oxide pathway, on hemodynamics and organ functions in human septic shock.

DESIGN

Prospective, randomized, controlled, open-label, pilot study.

SETTING

Multidisciplinary intensive care unit of a university hospital.

PATIENTS

Twenty patients with septic shock diagnosed <24 hrs before randomization.

INTERVENTIONS

Patients were randomized 1:1 to receive either MB (MB group, n = 10) or isotonic saline (control group, n = 10), adjunctive to conventional treatment. MB was administered as an intravenous bolus injection (2 mg/kg), followed 2 hrs later by infusion at stepwise increasing rates of 0.25, 0.5, 1, and 2 mg/kg/hr that were maintained for 1 hr each. During infusion, mean arterial pressure was maintained between 70 and 90 mm Hg, while attempting to reduce concurrent adrenergic support.

MEASUREMENTS AND MAIN RESULTS

Hemodynamics and organ function variables were assessed over a 24-hr period, and the survival rate at day 28 was noted. Infusion of MB prevented the stroke volume and the left-ventricular stroke work indexes from falling and increased mean arterial pressure. Compared with the control group, MB reduced the requirement for norepinephrine, epinephrine, and dopamine by as much as 87%, 81%, and 40%, respectively. Oxygen delivery remained unchanged in the MB group and decreased in the control group. MB also reduced the body temperature and the plasma concentration of nitrates/nitrites. Leukocytes and organ function variables such as bilirubin, alanine aminotransferase, urea, and creatinine were not significantly affected. Platelet count decreased in both groups. Five patients treated with MB survived vs. three patients receiving conventional treatment.

CONCLUSIONS

In human septic shock, continuously infused MB counteracts myocardial depression, maintains oxygen transport, and reduces concurrent adrenergic support. Infusion of MB appears to have no significant adverse effects on the selected organ function variables.

17beta-estradiol inhibition of NADPH oxidase expression in human endothelial cells

We investigated the hypothesis that the antiatherosclerotic effect of 17beta-estradiol (E2) is due to a shift in the nitric oxide (NO)/superoxide (O2-) balance in the vessel wall, thereby increasing the bioavailability of NO. In human umbilical vein cultured endothelial cells, E2 (1-100 nmol/l), but not 17alpha-estradiol, caused a time- and concentration-dependent decrease in expression of the NADPH oxidase subunit gp91phox (up to 60% inhibition at both the mRNA and protein level). This effect was prevented by coincubation with the estrogen receptor antagonists tamoxifen and ICI 182,780 (1 micromol/l each). Within the same concentration range, E2 also up-regulated endothelial nitric oxide synthase expression ( approximately twofold). Moreover, preincubation of the cells with E2 or a gp91phox antisense oligonucleotide significantly decreased their capacity to generate O2- on phorbol ester stimulation (i.e., assembly of the active NADPH oxidase complex). Blockade of NO synthase activity, on the other hand, had no effect on phorbol ester-stimulated O2- formation. In addition, E2 (100 nmol/l) inhibited the increase in adhesion molecule and chemokine expression in cells exposed to cyclic strain. Cyclic strain enhanced endothelial O2- formation, thereby offsetting the inhibitory effect of NO on the expression of these gene products. E2 thus seems to act as an antioxidant at the genomic level which by improving the NO/O2- balance normalizes expression of proatherosclerotic gene products in endothelial cells.

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.

Protective effects of hypercapnic acidosis on ventilator-induced lung injury

To investigate whether respiratory acidosis modulates ventilator-induced lung injury (VILI), we perfused (constant flow) 21 isolated sets of normal rabbit lungs, ventilated them for 20 min (pressure controlled ventilation [PCV] = 15 cm H(2)O) (Baseline) with an inspired CO(2) fraction adjusted for the partial pressure of CO(2) in the perfusate (PCO(2) approximately equal to 40 mm Hg), and then randomized them into three groups. Group A (control: n = 7) was ventilated with PCV = 15 cm H(2)O for three consecutive 20-min periods (T1, T2, T3). In Group B (high PCV/normocapnia; n = 7), PCV was given at 20 (T1), 25 (T2), and 30 (T3) cm H(2)O. The targeted PCO(2) was 40 mm Hg in Groups A and B. Group C (high PCV/hypercapnia; n = 7) was ventilated in the same way as Group B, but the targeted PCO(2) was approximately equal to 70 to 100 mm Hg. The changes (from Baseline to T3) in weight gain (Delta WG: g) and in the ultrafiltration coefficient (Delta K(f) = gr/min/ cm H(2)O/100g) and the protein and hemoglobin concentrations in bronchoalveolar lavage fluid (BALF) were used to assess injury. Group B experienced a significantly greater Delta WG (14.85 +/- 5.49 [mean +/- SEM] g) and Delta K(f) (1.40 +/- 0.49 g/min/cm H(2)O/100 g) than did either Group A (Delta WG = 0.70 +/- 0.43; Delta K(f) = 0.01 +/- 0.03) or Group C (Delta WG = 5.27 +/- 2.03 g; Delta K(f) = 0.25 +/- 0.12 g/min/cm H(2)O/ 100 g). BALF protein and hemoglobin concentrations (g/L) were higher in Group B (11.98 +/- 3.78 g/L and 1.82 +/- 0.40 g/L, respectively) than in Group A (2.92 +/- 0.75 g/L and 0.38 +/- 0.15 g/L) or Group C (5.71 +/- 1.88 g/L and 1.19 +/- 0.32 g/L). We conclude that respiratory acidosis decreases the severity of VILI in this model.

*NO, RSNO, ONOO-, NO+, *NOO, NOx--dynamic regulation of oxidant scavenging, nitric oxide stores, and cyclic GMP-independent cell signaling

Following its release from nitric oxide synthase, nitric oxide seldom perfuses the cytosol; rather this reactive mediator quickly interacts with available target molecules proximate to its site of release. Within the cell, virtually every component, low-molecular-weight oxidants and reductants, proteins, lipids, sugars, and nucleic acids can be modified by nitrogen oxides thus acting as potential targets for reactive nitrogen oxides. Adducts formed by nitrogen oxides often modulate the cellular activities of the target molecules, and these modified molecules may be differentially metabolized or localized. The formation of nitrogen oxide adducts can be a reversible process, and the reactive nitrogen species released may be specifically oxidized or reduced during the process. Recently, numerous studies have demonstrated that reversible nitration of cellular proteins acts to transduce molecular signals regulating such diverse processes as muscle contraction, neurotransmission, protein metabolism, and apoptosis. The vast numbers of molecules that undergo biologically relevant interactions with nitrogen oxides imply that the cellular concentration of nitrosated and nitrated species may effectively comprise a reserve or cellular store. Potentially, these nitroso reserves function as critical components of the overall redox status of the intracellular environs. Understanding the dynamic regulation of nitric oxide/nitrogen oxides release from these stores is likely to provide clues important in resolving the complex pathophysiology of poorly understood multifactorial disorders, including neurodegeneration, multiorgan failure, cardiomyopathy, and septic shock.

Aging-related expression of inducible nitric oxide synthase and markers of tissue damage in the rat penis

Erectile dysfunction in the aging male results in part from the loss of compliance of the corpora cavernosal smooth muscle due to the progressive replacement of smooth muscle cells by collagen fibers. We have examined the hypothesis that a spontaneous local induction of inducible nitric oxide synthase (iNOS) expression and the subsequent peroxynitrite formation occurs in the penis during aging and that this process is accompanied by a stimulation of smooth muscle apoptosis and collagen deposition. The penile shaft and crura were excised from young (3-5 mo old) and old (24-30 mo old) rats, with or without perfusion with 4% formalin. Fresh tissue was used for iNOS and proteasome 2C mRNA determinations by reverse transcription polymerase chain reaction assay, ubiquitin mRNA by Northern blot, and iNOS protein by Western blot. Penile sections from perfused animals were embedded in paraffin and immunostained with antibodies against iNOS and nitrotyrosine, submitted to the TUNEL assay for apoptosis, or stained for collagen, followed by image analysis quantitation. A 4.1-fold increase in iNOS mRNA was observed in the old versus young tissues, paralleled by a 4.9-fold increase in iNOS protein. The proteolysis marker, ubiquitin, was increased 1.9-fold, whereas a related gene, proteasome 2c, was not significantly affected. iNOS immunostaining was increased 3.6-fold in the penile smooth muscle of the old rats as compared with the young rats. The peroxynitrite indicator nitrotyrosine was increased by 1.6-fold, accompanied by a 3.6-fold increase in apoptotic cells and a 2.0-fold increase in collagen fibers in the old penis. In conclusion, aging in the penis is accompanied by an induction of iNOS and peroxynitrite formation that may lead to the observed increase in apoptosis and proteolysis and may counteract a higher rate of collagen deposition in the old penis.

Metabolism 2000: the emperor needs new clothes

Metabolism is one of the corner stones of nutritional science. As biology enters the post-genomic era and with functional genomics beginning to takeoff, we anticipate that the study of metabolism will play an increasingly important role in helping to link advances made via the reductionist paradigm, that has been so successful in molecular and cellular biology, with those emerging from observational studies in animals and human subjects. A reconstructive metabolically-focused approach offers a timely paradigm for enhancing the elegance of nutritional science. Here we give particular attention to the use of tracers as phenotyping tools and discuss the application of our metaprobe concepts with respect to some novel features of metabolism, including 'underground metabolism', 'metabolic hijacking', 'catalytic promiscuity' and 'moonlighting proteins'. The opportunities for enhancing the study of metabolism by new and emerging technologies, and the importance of the interdisciplinary research enterprise are also touched upon. We conclude that: (1) the metaprobe concepts and approach, discussed herein, potentially yield a quantitative physiological (metabolic) phenotype against which to elaborate partial or focused genotypes; (2) physiological (metabolic) phenotypes which have a whole-body or kinetically-discernible inter-organ tissue-directed metabolic signature are an ideal target for this directed tracer-based definition of the 'functional' genotype; (3) metabolism, probed with tracer tool kits suitable for measuring rates of turnover, change and conversion, becomes in the current sociology of the 'Net', like AOL, Yahoo. Alta Vista, Lycos or Ask Jeeves, the portal for an exploration of the metabolic characteristics of the 'Genomics Internet'.

Evidence for dual effects of nitric oxide in the forced swimming test and in the tail suspension test in mice

L-Arginine (L-Arg), a substrate for nitric oxide synthase (NOS) at a dose of 250-500 mg/kg, i.p., significantly reduced the duration of immobility both in the forced swimming test (FST) and in the tail suspension test (TST), two models of depression in mice, without changing locomotion in an open field. Paradoxically, a similar effect was observed with the administration of N(G)-nitro-L-arginine (L-NNA) (0.3-10 mg/kg, i.p.), an inhibitor of NOS. However, higher doses of L-Arg (750-1000 mg/kg) and L-NNA (30 mg/kg) did not produce any anti-immobility effect in FST and TST. The inactive isomers D-Arg (100-1000 mg/kg, i.p.) and D-NNA (0.3-30 mg/kg, i.p.) did not affect immobility duration in either the FST and TST. Preadministration of L-NNA (30 mg/kg, i.p.), but not of D-NNA completely blocked the anti-immobility effect of L-Arg (500 mg/kg, i.p.) in the FST. Similarly, L-Arg (750 mg/kg, i.p.), but not D-Arg blocked the anti-immobility effect of L-NNA (3 mg/kg, i.p.) in the FST. The results indicate that either the synthesis of NO or the inhibition of its synthesis may produce antidepressant-like effects when assessed in the FST and TST. The physiological meaning of this finding is still obscure, but it could indicate that NO has a dual role in the modulation of depression.

Protection against hemorrhagic shock in mice genetically deficient in poly(ADP-ribose)polymerase

Hemorrhagic shock (HS) and resuscitation leads to widespread production of oxidant species. Activation of the enzyme poly(ADP-ribose) polymerase (PARP) has been shown to contribute to cell necrosis and organ failure in various disease conditions associated with oxidative stress. We tested the hypothesis whether PARP activation plays a role in the multiple organ dysfunction complicating HS and resuscitation in a murine model of HS and resuscitation by using mice genetically deficient in PARP (PARP(-/-)) and their wild-type littermates (PARP(+/+)). Animals were bled to a mean blood pressure of 45 mmHg (1 mmHg = 133 Pa) and resuscitated after 45 min with isotonic saline (2x volume of shed blood). There was a massive activation of PARP, detected by poly(ADP-ribose) immunohistochemistry, which localized to the areas of the most severe intestinal injury, i.e., the necrotic epithelial cells at the tip of the intestinal villi, and colocalized with tyrosine nitration, an index of peroxynitrite generation. Intestinal PARP activation resulted in gut hyperpermeability, which developed in PARP(+/+) but not PARP(-/-) mice. PARP(-/-) mice were also protected from the rapid decrease in blood pressure after resuscitation and showed an increased survival time, as well as reduced lung neutrophil sequestration. The beneficial effects of PARP suppression were not related to a modulation of the NO pathway nor to a modulation of signaling through IL-6, which similarly increased in both PARP(+/+) and PARP(-/-) mice exposed to HS. We propose that PARP activation and associated cell injury (necrosis) plays a crucial role in the intestinal injury, cardiovascular failure, and multiple organ damage associated with resuscitated HS.