Escherichia coli-induced inhibition of endothelium-dependent relaxation and gene expression and release of nitric oxide is attenuated by chronic alcohol ingestion

Ethanol attenuates vasorelaxation via inhibition of inducible nitric oxide synthase in rat artery exposed to interleukin-1β

Nitric oxide produced by inducible nitric oxide synthase (iNOS) regulates sepsis-induced hypotension. During septic shock, interleukin (IL)-1β is synthesized in endothelial cells and smooth muscle cells by endotoxin. Ethanol (EtOH) suppresses endotoxin-induced hypotension. The present study aimed to elucidate the effect of EtOH on gradual relaxation and iNOS expression induced by IL-1β in isolated rat superior mesenteric arteries (SMAs). Exposure to IL-1β-induced contraction in SMA rings, followed by a gradual relaxation of phenylephrine precontracted tone. Contraction was abolished by indomethacin (IM), cycloheximide (Chx), and endothelium denudation. In contrast, the gradual relaxation was abolished by NOS inhibitors, Chx, endothelium denudation, and inhibited by EtOH (50 and 100 mM). However, IM had no effect on relaxation. Western blot analysis demonstrated that iNOS expression was induced by IL-1β and was inhibited by EtOH and endothelium denudation. Furthermore, messenger RNA expression of iNOS, but not endothelial NOS, was inhibited by EtOH. These data suggest that IL-1β-induced contraction is mediated by thromboxane A2, whereas IL-1β-induced relaxation occurs via NO derived from iNOS. The endothelium plays an important role in vasorelaxation. Taken together, EtOH inhibits IL-1β-mediated vasorelaxation by suppressing endothelium iNOS expression. This study provides the first evidence of EtOH -induced inhibition of IL-1β-mediated vasorelaxation.

Evidence for the Involvement of RhoA Signaling in the Ethanol-Induced Increase in Intestinal Epithelial Barrier Permeability

In this work, we investigated the potential role of the small G protein RhoA in ethanol-induced tight junction (TJ) protein disassembly and increased intestinal epithelial barrier (IEB) permeability. Our study used Caco-2 cells as an in vitro IEB model and RhoA short hairpin RNA (shRNA) interference to establish whether RhoA plays a role in ethanol-induced TJ opening. RhoA shRNA interference partially inhibited epithelial leakage and restored normal transepithelial electrical resistance (TEER) values in the IEB. Moreover, RhoA shRNA interference prevented a shift in occludin distribution from insoluble to soluble fractions. Additionally, RhoA shRNA interference inhibited the ethanol-induced expression of zonula occludens-1 (ZO-1). Finally, RhoA shRNA interference inhibited an ethanol-induced increase in RhoA activity. The contributions of RhoA to an ethanol-induced increase in IEB permeability are associated with TJ disassembly.

Vascular actions of nitric oxide as affected by exposure to alcohol

Vasodilator substances liberated from endothelial cells, mainly nitric oxide (NO), play important roles in physiologically regulating blood flow and blood pressure and preventing pathological vascular damage. Impairment of these actions promotes the genesis of cardiovascular diseases such as hypertension, cerebral and cardiac hypoperfusion, impaired vasodilatation and atherosclerosis. Low concentrations of alcohol induce increased release of NO from the endothelium due to activation and expression of NO synthase (NOS). In contrast, administration of high concentrations of alcohol or its chronic ingestion impairs endothelial functions in association with reduced NO bioavailability. The endogenous NOS inhibitor asymmetric dimethylarginine may participate in decreased synthesis of NO. Chronic alcohol intake also impairs penile erectile function possibly by interfering with endothelial, but not nitrergic nerve, function. This review article summarizes the vascular actions of NO derived from endothelial and neuronal NOS as affected by alcohol, other than wine, and acetaldehyde in healthy individuals, human materials and various experimental animals.

Nitric oxide-mediated intestinal injury is required for alcohol-induced gut leakiness and liver damage

BACKGROUND

Alcoholic liver disease (ALD) requires endotoxemia and is commonly associated with intestinal barrier leakiness. Using monolayers of intestinal epithelial cells as an in vitro barrier model, we showed that ethanol-induced intestinal barrier disruption is mediated by inducible nitric oxide synthase (iNOS) upregulation, nitric oxide (NO) overproduction, and oxidation/nitration of cytoskeletal proteins. We hypothesized that iNOS inhibitors [NG-nitro-l-arginine methyl ester (l-NAME), l-N(6)-(1-iminoethyl)-lysine (l-NIL)] in vivo will inhibit the above cascade and liver injury in an animal model of alcoholic steatohepatitis (ASH).

METHODS

Male Sprague-Dawley rats were gavaged daily with alcohol (6 g/kg/d) or dextrose for 10 weeks +/- l-NAME, l-NIL, or vehicle. Systemic and intestinal NO levels were measured by nitrites and nitrates in urine and tissue samples, oxidative damage to the intestinal mucosa by protein carbonyl and nitrotyrosine, intestinal permeability by urinary sugar tests, and liver injury by histological inflammation scores, liver fat, and myeloperoxidase activity.

RESULTS

Alcohol caused tissue oxidation, gut leakiness, endotoxemia, and ASH. l-NIL and l-NAME, but not the d-enantiomers, attenuated all steps in the alcohol-induced cascade including NO overproduction, oxidative tissue damage, gut leakiness, endotoxemia, hepatic inflammation, and liver injury.

CONCLUSIONS

The mechanism we reported for alcohol-induced intestinal barrier disruption in vitro - NO overproduction, oxidative tissue damage, leaky gut, endotoxemia, and liver injury - appears to be relevant in vivo in an animal model of alcohol-induced liver injury. That iNOS inhibitors attenuated all steps of this cascade suggests that prevention of this cascade in alcoholics will protect the liver against the injurious effects of chronic alcohol and that iNOS may be a useful target for prevention of ALD.

Oats supplementation prevents alcohol-induced gut leakiness in rats by preventing alcohol-induced oxidative tissue damage

We reported previously that oats supplementation prevents gut leakiness and alcoholic steatohepatitis (ASH) in our rat model of alcoholic liver disease. Because oxidative stress is implicated in the pathogenesis of both alcohol-induced gut leakiness and ASH, and because oats have antioxidant properties, we tested the hypothesis that oats protect by preventing alcohol-induced oxidative damage to the intestine. Male Sprague-Dawley rats were gavaged for 12 weeks with alcohol (starting dose of 1 g/kg increasing to 6 g/kg/day over the first 2 weeks) or dextrose, with or without oats supplementation (10 g/kg/day). Oxidative stress and injury were assessed by measuring colonic mucosal inducible nitric-oxide synthase (iNOS) (by immunohistochemistry), nitric oxide (colorimetric assay), and protein carbonylation and nitrotyrosination (immunoblotting). Colonic barrier integrity was determined by assessing the integrity of the actin cytoskeleton (immunohistochemistry) and the integrity of tight junctions (electron microscopy). Oats supplementation prevented alcohol-induced up-regulation of iNOS, nitric oxide overproduction in the colonic mucosa, and increases in protein carbonyl and nitrotyrosine levels. This protection was associated with prevention of ethanol (EtOH)-induced disorganization of the actin cytoskeleton and disruption of tight junctions. We conclude that oats supplementation attenuates EtOH-induced disruption of intestinal barrier integrity, at least in part, by inhibiting EtOH-induced increases in oxidative stress and oxidative tissue damage. This inhibition prevents alcohol-induced disruption of the cytoskeleton and tight junctions. This study suggests that oats may be a useful therapeutic agent--a nutraceutical--for the prevention of alcohol-induced oxidative stress and organ dysfunction.

Ethanol metabolism is not required for inhibition of LPS-stimulated transcription of inducible nitric oxide synthase

We examined the effect of inhibition of ethanol metabolism on ethanol-mediated suppression of Escherichia coli endotoxin (LPS-induced upregulation of transcription and release of inducible nitric oxide synthase (iNOS) and tumor necrosis factor alpha (TNFalpha) from rat alveolar macrophages (AM) in vivo. Ethanol (3.45 and 5.5 g/kg/IP) and t-butanol (3.7 g/kg, IP), given 30 min before intratracheal administration of LPS (1.0 mg/kg), inhibited the upregulation of iNOS mRNA and protein, determined by competitor equalized RT-PCR and Western immunoblot, respectively, but not TNFalpha mRNA in AM obtained 2 h after LPS administration by bronchoalveolar lavage (BAL). However, ethanol and t-butanol inhibited LPS-stimulated nitrate and nitrite (RNI) and TNFalpha protein in BAL fluid. Pretreatment of rats with 4-methylpyrazole (100 mg/kg, IP) 2 h before, or disulfiram 30 min before, administration of ethanol (3.45 g/kg, IP) failed to attenuate the inhibitory effect on iNOS mRNA or protein. t-Butyl hydroperoxide (100 mg/kg, IP) given to rats 30 min before administration of LPS enhanced LPS-mediated upregulation of iNOS mRNA and TNFalpha protein in AM and BAL fluid. The inhibitory effect of ethanol on iNOS mRNA was not mediated by an interaction with elevated levels of circulating corticosterone because pretreatment of rats with RU-38486 (100 mg/kg, IM), which inhibited prednisolone (50 mg/kg, IM), induced suppression of LPS-stimulated iNOS mRNA, and failed to attenuate ethanol-mediated inhibition of LPS-stimulated iNOS mRNA in AM. We conclude that metabolism of ethanol to acetaldehyde via alcohol dehydrogenase is not required for ethanol-mediated suppression of LPS-induced iNOS transcription and TNFalpha synthesis/release in AM. Moreover, an interaction of ethanol or acetaldehyde with circulating corticosterone is not involved in ethanol-mediated attenuation of LPS-stimulated iNOS mRNA or protein or TNFalpha protein in the lung. Speculatively, because oxidation of t-butanol to t-butylhydroperoxide results in activation, rather than inhibition, of iNOS and TNF-alpha, the reported ethanol-mediated enhancement of iNOS mRNA may result from the action of the hydroxyethyl radical.

Role of PKC and tyrosine kinase in ethanol-mediated inhibition of LPS-inducible nitric oxide synthase

Ethanol increases human and animal susceptibility to opportunistic lung infections in part by suppression of endotoxin (LPS) and bacteria-mediated upregulation of inducible nitric oxide synthase (iNOS) in alveolar macrophages (AM). LPS and cytokine-induced NOS mRNA are dependent on NF-kappaB/Rel (NFkappaB) and Activator Protein-1 (AP-1), which are regulated in turn by protein kinase C and tyrosine kinase-dependent phosphorylation. ETOH does not directly inhibit NFkappaB or AP-1, in vivo, but rather inhibits LPS-induced activation of the MEKK/MAP kinase system and inhibition of inhibitory protein IkappaBalpha required for formation of AP-1 and NFkappaB, respectively. in AM. Both transcription factors are involved iNOS mRNA transcription. LPS-induced upregulation of MEKK/MAP tyrosine kinase upregulates NADPH oxidase activity and oxygen free radical formation required for activation of NFkappaB and AP-1 and phosphorylation of IkappaBalpha. LPS downregulates endogenous calcium-sensitive PKC isozymes (PKCdelta), which repress iNOS mRNA expression. ETOH inhibits LPS-induced upregulation of iNOS mRNA by preventing its ability to decrease PKCdelta and upregulate tyrosine kinase-mediated phosphorylation. This effect of ETOH is prevented by inhibitors of PKC and tyrosine kinase. The data support the hypothesis that ETOH inhibits LPS-induced upregulation of iNOS mRNA by interfering with the phosphorylation processes involved in activation of the nuclear transcription factors NFkappaB and AP-1.

Alcohol intoxication and withdrawal: the role of nitric oxide

Nitric oxide is an important messenger in the central nervous system and several types of evidence suggest that it mediates various alcohol effects. Treatment with a nitric oxide synthase inhibitor enhances the acute central depressant or anesthetic effect of alcohol and decreases some stimulatory effects of alcohol withdrawal after chronic alcohol treatment. Conversely, treatment with a nitric oxide donor inhibits the anesthetic effect of alcohol, blocks the effect of the nitric oxide synthase inhibitor on alcohol anesthesia, and enhances the severity of some alcohol withdrawal signs. These results indicate that changes in nitric oxide synthesis mediate some aspects of alcohol intoxication and withdrawal and that nitric oxide systems represent an important therapeutic target for the development of agents to treat alcoholism and alcohol intoxication.

Splenic sympathetic response to endotoxin is blunted in the fetal alcohol-exposed rat: role of nitric oxide

This study was designed to test the hypothesis that nitric oxide (NO) mediates the blunted splenic sympathetic response to lipopolysaccharide (endotoxin) that occurs in young rats exposed to alcohol in utero (FAE). The subjects, 26-29-day-old rats, were progeny of pregnant dams fed an alcohol diet (35% of the calories were derived from ethanol) or their control and pair-fed (PFC) cohorts. We examined the effects of lipopolysaccharide (LPS) (0.5 mg/kg, i.p.) on splenic norepinephrine (NE) turnover, an index of sympathetic neural activity, splenic inducible NO synthase (iNOS) protein immunoreactivity, and NO metabolites nitrite/nitrate concentrations in plasma. In response to LPS, splenic NE turnover was increased by more than twofold in the PFC groups, but the increase did not occur in their FAE cohorts. The blockade of NOS with L-NAME (30 mg/kg, i.p.) reversed this difference. In both the PFC and FAE rats, basal levels of splenic iNOS protein immunoreactivity were equally barely detected and plasma NO metabolite levels were relatively low (25 microM in both groups). In response to LPS, however, iNOS protein displayed a marked increase in the PFC group and an even greater increase (by close to threefold) in the FAE rats. LPS also substantially increased plasma NO metabolite levels by close to eightfold in the control groups, but by 15-fold in their FAE cohorts compared to the basal levels. These findings support the hypothesis that in the FAE rat, an augmented NO formation accounts for the blunted sympathetic response to endotoxin.

Binge ethanol-induced brain damage in rats: effect of inhibitors of nitric oxide synthase

Testing the possible role of endogenous nitric oxide (NO) in the neurotoxicity of ethanol, we examined how two different NO synthase (NOS) inhibitors affected the extent cerebrocortical and olfactory neuronal damage in a modified "binge intoxication" rat model (Collins et al., Alcohol Clin. Exp. Res. 20:284-292, 1996). Male rats intragastrically fed ethanol (6.5 to 12 g/kg/day) in nutrient solution three times daily for 4 days also received NG-nitro-L-arginine methyl ester by chronic intracerebroventricular infusion or 7-nitro-indazole by daily intraperitoneal injection; control rats were given nutrient solution only and/or vehicles. Blood ethanol levels did not differ among the ethanol-treated groups. The amount of ethanol-dependent neuronal degeneration in the entorihinal cortex, dentate gyrus, and olfactory bulb glomeruli--visualized with the de Olmos cupric silver stain and quantitatively assessed in the binge-intoxicated rats--was either unchanged or significantly increased by the NOS inhibitors. Although the efficacies of the inhibitors cannot be directly compared because of various NOS forms were probably inhibited to differing extents, the results do not support the idea that endogenous NO is a neurotoxic mediator of ethanol's effects. Rather NO may have a modest neuroprotectant role in this model of early brain damage induced by ethanol. In addition, the NOS that is localized histochemically as NADPH diaphorase was present primarily in regions and/or cells not damaged by binge ethanol treatment. Assuming that NADPH diaphorase represents most of the NO forming enzyme(s) this suggests a transcellular mechanism for NO. A further observation was that hippocampal CA pyramidal neuron degeneration was extensive in rats infused centrally with NG-nitro-L-arginine methyl ester.

Ethanol suppresses endotoxin but not platelet activating factor-induced hypotension and nitric oxide

Ethanol (ETOH) inhibits the immune response to endotoxemia. The early stage of endotoxin (LPS)-induced shock is associated with an acute phase cardiovascular depression (APCD). Release of platelet activating factor (PAF) and tumor necrosis factor alpha (TNF alpha) with upregulation of nitric oxide (NO) production may initiate the APCD. Since ETOH inhibits induction of NO synthase (iNOS) mNRA by LPS, we postulate that ETOH may mask the APCD associated with endotoxemia. To test this, Sprague-Dawley rats (280-320 g, n = 5-6/group) were given LPS [0.75 mg/kg, intravenously (i.v.)] or PAF (10 to 150 micrograms/kg, i.v.) 30 min after administration of sterile saline (PBS), BN-5073 a mixed PAF antagonist (0.50 microgram/kg, i.v.), or ETOH [2.2-5.5 g/kg, intraperitoneally (i.p.)]. Cardiovascular parameters and plasma concentrations of nitrate and nitrite (RNI), ETOH, TNF alpha, and neutrophil (PMN) generation of RNI were measured. LPS and PAF both produced APCD. LPS-induced APCD was associated with tachycardia, elevated plasma TNF alpha and RNI, and ex vivo generation of RNI by PMNs. ETOH and BN-50730 prevented LPS-induced APCD and increases in RNI and TNF alpha. ETOH, however, increased the mortality associated with APCD. PAF produced only hypotension, bradycardia and elevated plasma levels of TNF alpha. ETOH and LNMMA did not affect PAF-induced APCD. BN-50730 inhibited PAF-induced APCD and plasma TNF alpha. We conclude that 1) ETOH inhibits the APCD and induction of NO characteristic of endotoxemia and 2) ETOH-induced suppression of LPS-mediated APCD may be mediated in part by suppression of release of intracellular PAF. Ethanol may increase the morbidity and mortality of endotoxemia by masking the hypotension and humoral changes characteristic of early endotoxemia thereby delaying appropriate therapy and by diminution of the protective effects of endogenous NO.

Nitric oxide and liver injury in alcohol-fed rats after lipopolysaccharide administration

Earlier studies showed that alcohol-fed animals were more susceptible than controls to injurious effects of endotoxin. Increased superoxide radical production by hepatocyte organelles, Kupffer cells, and neutrophils from alcohol-fed animals has been well documented. In this study, electron paramagnetic resonance spectroscopy was used to detect nitrosyl protein complexes indicating nitric oxide (.NO) production. We showed that the concentrations of nitrosyl complexes in whole blood and in liver tissues of alcohol-fed rats treated with lipopolysaccharide (alc + LPS), increased 3-fold, compared with those from rats on control diet treated with LPS (con+LPS). Electron paramagnetic resonance spectra of whole blood and liver tissues from the alc + LPS-treated group exhibited features characteristic of hemoglobin nitrosyl complexes. Plasma levels of the hepatic ASTs and ALTs from the alc + LPS-treated group were increased 2- to 3-fold, compared with those from the con+LPS-treated group. Inhibition of .NO production of aminoguanidine treatment attenuated plasma hepatic enzyme levels in the alc + LPS-treated group. Thus, under the conditions of elevated inflammatory oxidative states caused by chronic alcohol feeding, endotoxin treatment enhanced liver injury as a result of the actions of .NO, and/or the cytotoxic species derived from .NO.

Alcohol stimulates ACTH secretion in the rat: mechanisms of action and interactions with other stimuli

This review discusses some of the mechanisms through which alcohol (EtOH) alters the activity of the hypothalamic-pituitary-adrenal (HPA) axis. In adult rats, acute EtOH treatment increases plasma ACTH and corticosteroids levels primarily by stimulating the release of corticotropin-releasing factor (CRF) and possibly vasopressin (VP) from nerve terminals in the median eminence. Increased CRF gene transcription in the hypothalamus may also be important. The HPA axis remains activated during chronic EtOH exposure, although habituation may take place. Changes in the responsiveness of hypothalamic neurons, a phenomenon itself dependent in part on a number of intermediate secretagogues, as well as decreased pituitary responsiveness to VP, all play a role. Finally, the activity of the HPA axis is influenced by exposure to EtOH during embryonic development, with mature offspring showing hyporesponsiveness to many stimuli. These altered responses appear to be caused in part by changes in the synthesis/release CRF, possibly under the influence of nitric oxide. CRF, VP, ACTH, and corticosteroids are important regulators of the immune system, behavior, metabolic pathways, and reproductive parameters. Alcohol therefore may influence such functions through the pathological secretion of these hormones. A better understanding of the mechanisms through which the drug alters their release thus may permit the development of therapies designed to alleviate some of the consequences of alcoholism.

Gender differences in the effect of prenatal alcohol exposure on the hypothalamic-pituitary-adrenal axis response to immune signals

Immature (3 week old) rat offspring of alcohol (E)-fed dams show a blunted ACTH response to immune signals such as interleukin-1 beta (IL-1 beta) and endotoxin (LPS). In contrast, mature offspring respond to physical stresses with an exaggerated activation of their hypothalamic-pituitary-adrenal (HPA) axis. The present work was aimed at determining if there was a differential influence of prenatal E exposure on the HPA axis responses to various stressors or if, alternatively, sexual maturation modified these responses. When administered IL-1 beta at 5 weeks age, E-treated intact male offspring released less ACTH, compared to control (C) or pair-fed (PF) animals. However, they showed an augmented response to LPS and a local inflammatory process induced by turpentine injection. At this same age, intact E females secreted significantly more ACTH in response to IL-1 beta, LPS and turpentine, than C or PF offspring. By 9 weeks of age, both E males and E females exhibited larger (p < .05) ACTH responses to all three immune stimuli. In order to determine whether sex steroids modulate the influence of E in females, ovariectomy was done prior to puberty. This treatment decreased the difference in the ACTH released by E and C rats in response to IL-1 beta, LPS and turpentine. These results show that while immature rats exposed to E prenatally released less ACTH in response to cytokines than C or PF animals did, this response was qualitatively reversed after puberty. At that time, the larger amounts of ACTH secreted by E offspring, compared to the other groups, were reminiscent of the hyperactive response of the HPA axis when these offspring were exposed to physical stress. Interestingly, removal of circulating ovarian steroids prevented the influence of E from being exerted. This suggests the presence of a functional relationship between the pathways influenced by prenatal E and those influenced by female sex steroids, that are important in regulating the activity of the HPA axis.

Adult male rats exposed to an alcohol diet exhibit a blunted adrenocorticotropic hormone response to immune or physical stress: possible role of nitric oxide

Intact adult male rats fed an alcohol [ethanol (EtOH)] diet for 10 days show blunted adrenocorticotropic hormone (ACTH) release in response to immune signals such as the cytokine interleukin-1 beta (IL-1 beta) and endotoxin [lipopolysaccharide (LPS)], as well as to physical stress (mild electroshocks). The mechanisms responsible for this effect remain poorly understood, but we have recently reported that decreased pituitary responsiveness to vasopressin (VP) might play a role. In naive rats, nitric oxide (NO) exerts a restraining influence on the response of the hypothalamic-pituitary (H-P) axis to cytokines and VP. The ability of long-term EtOH treatment to increase glutamate receptors, and thus NO formation, prompted us to test the hypothesis that abnormally high NO concentrations might modulate the influence of the drug. Blockade of the activity of NO synthase (NOS), the enzyme responsible for NO formation, with the arginine derivative L-N omega nitro-L-arginine-methylester (L-NAME), augmented the ACTH response to IL-1 beta or LPS in both control (C) and EtOH-fed (E) rats. Indeed, after L-NAME treatment, ACTH concentrations were statistically comparable in C and E animals injected with endotoxin or a large dose of IL-1 beta. VP-induced ACTH secretion also became comparable in both experimental groups after blockade of NOS activity. In contrast, the decreased response of the H-P axis of E animals to shocks was only slightly ameliorated, compared with that of C rats. It is therefore possible that changes in the NOergic tone induced by alcohol play a role in the decreased response of the H-P axis to cytokines, possibly in part by altering the stimulatory action of VP on the corticotrophs. On the other hand, in E rats NO seems to exert only a minimal influence on the central nervous system circuits activated by shocks.

Nitro containing L-arginine analogs interfere with assays for nitrate and nitrite

We evaluated the effect of in vivo and in vitro administration of nitro-containing and nitro-deficient L-arginine-derived nitric oxide (NO) synthase inhibitors on the measurement of NO in plasma, urine and HEPES buffered physiologic salt solution (PSS) by ozone chemiluminescence and by the modified Griess reaction. In vivo administration of 1, 5, 25, 40 or 50 mg/kg of NG-nitro-L-or D-arginine methyl ester (LNAME, DNAME), NG-nitro-L-arginine (LNA) or aminoguanidine (AG) to rats and mice increased NO in urine and plasma as determined by chemiluminescence using 2.3% vanadium chloride in 2N HCI at 100 degrees C as the redox reagent. In vivo administration of 1 and 10 mg/kg/day of NG-imino-ethyl-L-ornithine (LNIO) or 3 amino-1,2,4 triazine (AT) reduced plasma and urine NO. Addition of LNAME, DNAME and LNA (100 nM to 1 mM) to the redox solution produced a concentration response curve for NO in the chemiluminescence assay similar to that produced by standard solutions of sodium nitrite and nitrate. LNMMA produced a small NO signal but only at concentrations equal to or exceeding 0.1 mM. LNIO, AT and AG did not give any NO signal even at concentrations exceeding 1 mM. Conversion of plasma or urine nitrate to nitrite with cadmium gave elevated values of plasma nitrite by the Greiss assay when LNAME or LNA was the NO synthase inhibitor. We conclude that in vivo and in vitro use of LNAME and LNA and in vivo use of high doses of aminoguanidine interfere with the assay of NO2- and NO3- with the modified Griess reaction and with chemiluminescence. We suggest that LNAME and LNA not be used in vivo or in vitro when total RNI is measured with these assays.

Nitric oxide production in experimental alcoholic liver disease in the rat: role in protection from injury

BACKGROUND & AIMS

Regulation of blood flow and oxygen supply are important pathogenetic factors in alcoholic liver disease. Because nitric oxide may have an important role, its effects on alcoholic liver injury were investigated.

METHODS

Rats were fed ethanol intragastrically with either saturated fat or corn oil. Spontaneous production of NO by liver nonparenchymal cells was compared in the two dietary groups. Two additional groups of rats fed corn oil and ethanol were treated with either an NO inhibitor (L-NAME) or supplemented with L-arginine. Liver pathology and plasma NO production were evaluated.

RESULTS

In the corn oil and ethanol group, a progressive decrease in liver nonparenchymal cell NO production and increased plasma NO levels were associated with liver injury. Reduced nicotinamide adenine dinucleotide phosphate diaphorase staining showed increased centrilobular staining of hepatocytes in the corn oil and ethanol group and L-NAME-treated group. Moreover, L-NAME increased the severity, whereas L-arginine supplementation completely prevented liver injury. In the saturated fat and ethanol group, in which there was no liver injury, the levels of NO2- in nonparenchymal supernatant were 5-10-fold higher than in the corn oil and ethanol group.

CONCLUSIONS

Decreased NO production by nonparenchymal cells may contribute to liver injury in ethanol-fed rats, and the compensatory increase in hepatocyte NO production may contribute to centrilobular liver injury.

Ethanol suppresses Mycobacteria tuberculosis-induced mRNA for nitric oxide synthase in alveolar macrophages, in vivo

Acute ingestion of alcohol [ethanol (ETOH)] adversely affects the immunocompetence of both naive individuals as well as chronic alcohol abusers. An increased incidence and severity of tuberculosis is found in chronic alcohol abusers. Nitric oxide (NO) produced by alveolar macrophages (AMs) may play a role in the in vitro killing of Mycobacterium avium and Mycobacterium tuberculosis (MTB). Moreover, tumor necrosis factor-alpha (TNF-alpha) is believed to be a primary cytokine mediator of NO production by AMs. Recent studies from our laboratory demonstrated that ETOH suppressed endotoxin-induced increases in both TNF-alpha and NO in AMs, in vivo. We tested the postulate that acute ingestion of ETOH can interfere with mycobacteria-induced upregulation of the NO system in AMs, in vivo. We show that heat-killed M. avium complex (MAC) and human virulent MTB instilled into rat lungs rapidly increased mRNA for inducible NO synthase II (iNOS) of AMs in fluid obtained by bronchoalveolar lavage (BAL fluid). This was associated with production of reactive nitrogen intermediates [(RNIs); NO2- and NO3-] in BAL fluid, lung homogenate, and AMs in the absence of a significant increase in BAL fluid TNF-alpha. A single dose of ETOH (5.5 g/kg, ip) administered 30 min before intratracheal administration of MAC or MTB attenuated both MAC and MTB-induced increases in RNI in BAL fluid, lung, and AMs, and the increase in mRNA for iNOS. Thus, mycobacteria upregulate iNOS mRNA and enhance RNI production by AMs without any increase in the production of TNF-alpha. Moreover, ETOH attenuates mycobacteria-induced upregulation of mRNA for iNOS and RNI production in the absence of ETOH-mediated suppression of TNF. Speculatively, ETOH-mediated inhibition of the AM NO system may offer an explanation for the increased severity of mycobacterial infections in alcoholics.

Selective inhibition of sympathetic nerve-mediated contraction by L-arginine in lipopolysaccharide-treated tail artery of rats

The effects of L-arginine on the adrenergic responses to either electrical transmural stimulation or phenylephrine were studied in isolated endothelium-denuded strips of rat tail arteries treated with lipopolysaccharide for 6 h in vitro. L-arginine did not relax the strips precontracted by phenylephrine. However, the adrenergic contractions induced by electrical transmural stimulation were significantly inhibited by the addition of L-arginine. This inhibitory effect was reversed by NG-nitro-L-arginine (a nitric oxide synthase inhibitor) or methylene blue (a soluble guanylate cyclase inhibitor) but was not affected by hemoglobin (a scavenger of nitric oxide). These results indicate that the adrenergic neurogenic contractions may be directly modulated by nitric oxide derived from the sympathetic nerves and/or neighboring cells in the lipopolysaccharide-treated rat tail arteries, and the nitric oxide production may be associated with the reduction of sympathetic tone in sepsis.

Ethanol suppresses LPS-induced mRNA for nitric oxide synthase II in alveolar macrophages in vivo and in vitro

Alcohol abuse increases the incidence and severity of opportunistic lung infections and pneumonias. Inducible nitric oxide (NO) synthase (iNOS II) and NO may be a pivotal system in the intracellular bactericidal activity of macrophages. We tested the hypothesis that acute administration of ethanol (ETOH) suppressed Escherichia coli endotoxin lipopolysaccharide (LPS) mediated upregulation of the iNOS II system in the lung of the rat, in vivo. We also tested the effect of ETOH on alveolar macrophage (AM) production of free NO using microelectrodes. Male Sprague-Dawley rats were given ETOH (5.5 g/kg, IP) 30 min. before giving intratracheal sterile phosphate buffered saline solution (PBS, 0.5 ml) or LPS (1 mg/kg in a total volume of 0.5 ml PBS). The isolated lungs were subjected to bronchoalveolar lavage (BAL) 3.5 hr. later. Aliquots of the BAL fluid were assayed for tumor necrosis factor alpha TNF alpha and reactive nitrogen intermediates (nitrate and nitrite) (RNI) with chemiluminescence. Aliquots of AM were incubated 1 hr ex vivo for spontaneous production of RNI or frozen and assayed for iNOS II mRNA with competitor exchange reverse transcriptase polymerase chain reaction (cERT-PCR). The lung was homogenized and assayed for RNI. LPS increased BAL fluid TNF alpha and RNI, lung RNI, and the spontaneous production of RNI by AM, ex vivo. These effects were inhibited by in vivo administration of inhibitors of iNOS II. LPS increased iNOS mRNA in AM. This was unaffected by iNOS inhibitors. ETOH suppressed LPS-induced BAL fluid TNF, iNOS mRNA and RNI production by AM and the lung.(ABSTRACT TRUNCATED AT 250 WORDS)