Antioxidant enzymes in intramural nerves of the opossum esophagus

Down syndrome and the enteric nervous system

Down syndrome (DS) is the most common chromosomal abnormality occurring in humans. Up to 77% of DS children have associated gastrointestinal (GI) abnormalities, which may be structural or functional in nature. Functional disturbances may, in turn, affect the outcome of corrective surgical procedures, prompting to caution. It is becoming clear that the processes affecting the enteric nervous system (ENS) in DS not only affect the micro-anatomy but also nerve function, and there is some histological evidence of ENS variations in both human and DS animal models. This suggests that developmental disorders of the ENS are probably fundamental to the functional GI disturbances encountered in patients with DS. The anomalous brain development, function and resulting intellectual impairment associated with DS appears to result from the genetic imbalance created by the trisomy of chromosome 21. The possible links between the brain, GI and ENS involvement are not as yet entirely clear. Neurotropic factors affecting brain development during embryogenesis are probably interlinked with ENS development, but the precise mechanism of how this occurs has yet to be established. This study explores what is known about the ENS dysfunction in DS and reviews the possible importance of chromosome 21 located and other genes in its etiology. Functional motor disturbances of the esophagus and colon are not uncommon and may be congenital or acquired in nature. The most prominent of these include esophageal dysmotility syndromes (e.g. achalasia, gastroesophageal reflux, dysphagia) as well as a higher incidence of chronic constipation and Hirschsprung's disease (HSCR) (2-15%) occurring in association with DS. Chromosome 21 itself is thought to be the site of a modifier gene for HSCR. Recently identified candidate genetic mechanisms provide unique insights into the genetic background of the neurological and cognitive disorders associated with DS. Although the role of the triplicated chromosome 21 and genetic dosage remain important, the additional role of other chromosome 21 genes in the etiology of ENS developmental anomalies remains undetermined and requires ongoing research.

Generation of nitric oxide in the opossum lower esophageal sphincter during physiological experimentation

Lipopolysaccharide (LPS), given in vivo, modulates opossum esophageal motor functions by inducing the inducible nitric oxide synthase (iNOS), which increases nitric oxide (NO) production. Superoxide, a NO scavenger, is generated during this endotoxemia. Superoxide is cleared by superoxide dismutase (SOD) and catalase (CAT) to protect the physiological function of NO. This study examined whether lower esophageal sphincter (LES) motility, NO release, and iNOS and nitrotyrosine accumulation in the LES are affected by LPS in vitro. Muscle strips from the opossum LES were placed in tissue baths containing oxygenated Krebs buffer. NO release was measured with a chemiluminescence NOx analyzer, and Western blots were performed to analyze iNOS and nitrotyrosine production. The percent change in resting LES tone after a 6-hour exposure to LPS was significantly increased compared to pretreatment values. The percent LES relaxation upon electrical stimulation was significantly decreased in the control group at 6 hours, indicating that the LPS treatment had an effect. The NO concentration in the tissue bath of LPS- treated muscle without nerve stimulation was significantly less than that of LPS treatment combined with SOD/CAT or SOD/CAT alone. iNOS and nitrotyrosine were detectable and increased over time in the LES muscle of both the control and LPS-treated groups. Antioxidant enzymes may play a role in regulating NO-mediated neuromuscular functions in the LES.

Free radicals and antioxidant systems in reflux esophagitis and Barrett's esophagus

AIM

Experimental studies suggest that free radicals are involved in acid and pepsin-induced damage of esophageal mucosa. The profile and balance between free radicals and antioxidant systems in human esophagitis are unknown.

METHODS

Superoxide anion and its powerful oxidant reaction with nitric oxide (peroxynitrite) generation were determined in esophageal mucosal biopsies from 101 patients with different gastro-esophageal reflux diseases and 28 controls. Activity of both superoxide dismutase (SOD) and catalase, and reduced glutathione (GSH) levels, were also assessed. Expression of Cu, ZnSOD, MnSOD and tyrosine-nitrated MnSOD were analyzed by Western blot and/or immunohistochemistry.

RESULTS

The highest levels of superoxide anion generation were found in patients with severe lesions of esophagitis. Peroxynitrite generation was intense in Barrett's biopsies, weaker in esophagitis and absent/weak in normal mucosa. Expression of Cu, ZnSOD and MnSOD isoforms were present in normal mucosa and increased according to the severity of the lesion, reaching the highest level in Barrett's esophagus. However, SOD mucosal activity significantly decreased in patients with esophagitis and Barrett's esophagus, which was, at least in part, due to nitration of its tyrosine residues. Catalase activity and GSH levels were significantly increased in mucosal specimens from patients with esophagitis and/or Barrett's esophagus.

CONCLUSION

A decrease in SOD antioxidant activity leading to increased mucosal levels of superoxide anion and peroxynitrite radicals may contribute to the development of esophageal damage and Barrett's esophagus in patients with gastroesophageal reflux. Administration of SOD may be a therapeutic target in the treatment of patients with esophagitis and Barrett's esophagus.

Free radicals and antioxidant systems in reflux esophagitis and Barrett’s esophagus

AIM: Experimental studies suggest that free radicals are involved in acid and pepsin-induced damage of esophageal mucosa. The profile and balance between free radicals and antioxidant systems in human esophagitis are unknown.

METHODS: Superoxide anion and its powerful oxidant reaction with nitric oxide (peroxynitrite) generation were determined in esophageal mucosal biopsies from 101 patients with different gastro-esophageal reflux diseases and 28 controls. Activity of both superoxide dismutase (SOD) and catalase, and reduced glutathione (GSH) levels, were also assessed. Expression of Cu,ZnSOD, MnSOD and tyrosine-nitrated MnSOD were analyzed by Western blot and/or immunohistochemistry.

RESULTS: The highest levels of superoxide anion generation were found in patients with severe lesions of esophagitis. Peroxynitrite generation was intense in Barrett’s biopsies, weaker in esophagitis and absent/weak in normal mucosa. Expression of Cu,ZnSOD and MnSOD isoforms were present in normal mucosa and increased according to the severity of the lesion, reaching the highest level in Barrett’s esophagus. However, SOD mucosal activity significantly decreased in patients with esophagitis and Barrett’s esophagus, which was, at least in part, due to nitration of its tyrosine residues. Catalase activity and GSH levels were significantly increased in mucosal specimens from patients with esophagitis and/or Barrett’s esophagus.

CONCLUSION: A decrease in SOD antioxidant activity leading to increased mucosal levels of superoxide anion and peroxynitrite radicals may contribute to the development of esophageal damage and Barrett’s esophagus in patients with gastroesophageal reflux. Administration of SOD may be a therapeutic target in the treatment of patients with esophagitis and Barrett’s esophagus.

Free radicals and antioxidant systems in reflux esophagitis and Barrett’s esophagus

AIM: Experimental studies suggest that free radicals are involved in acid and pepsin-induced damage of esophageal mucosa. The profile and balance between free radicals and antioxidant systems in human esophagitis are unknown.

METHODS: Superoxide anion and its powerful oxidant reaction with nitric oxide (peroxynitrite) generation were determined in esophageal mucosal biopsies from 101 patients with different gastro-esophageal reflux diseases and 28 controls. Activity of both superoxide dismutase (SOD) and catalase, and reduced glutathione (GSH) levels, were also assessed. Expression of Cu,ZnSOD, MnSOD and tyrosine-nitrated MnSOD were analyzed by Western blot and/or immunohistochemistry.

RESULTS: The highest levels of superoxide anion generation were found in patients with severe lesions of esophagitis. Peroxynitrite generation was intense in Barrett’s biopsies, weaker in esophagitis and absent/weak in normal mucosa. Expression of Cu,ZnSOD and MnSOD isoforms were present in normal mucosa and increased according to the severity of the lesion, reaching the highest level in Barrett’s esophagus. However, SOD mucosal activity significantly decreased in patients with esophagitis and Barrett’s esophagus, which was, at least in part, due to nitration of its tyrosine residues. Catalase activity and GSH levels were significantly increased in mucosal specimens from patients with esophagitis and/or Barrett’s esophagus.

CONCLUSION: A decrease in SOD antioxidant activity leading to increased mucosal levels of superoxide anion and peroxynitrite radicals may contribute to the development of esophageal damage and Barrett’s esophagus in patients with gastroesophageal reflux. Administration of SOD may be a therapeutic target in the treatment of patients with esophagitis and Barrett’s esophagus.

Slowing of intestinal transit by fat or peptide YY depends on beta-adrenergic pathway

Although the enteric reflex pathway triggered by volume distension is known to depend on an adrenergic nerve, it is not known whether the slowing of intestinal transit by fat or peptide YY (PYY) also depends on an adrenergic pathway. The aim of this study was to test the hypotheses that the slowing of transit by fat or PYY may depend on a beta-adrenergic pathway, and this adrenergic pathway may act via the serotonergic and opioid pathways previously observed for the slowing of transit by fat. Eighteen dogs were equipped with duodenal and midgut fistulas. The small intestine was compartmentalized into the proximal and distal half of gut. The role of adrenergic, serotonergic, and opioid pathways was then tested in the slowing of intestinal transit by fat, PYY, and norepinephrine. Intestinal transit results were compared as the cumulative percent marker of recovery over 30 min. We found that the slowing of transit by fat, PYY, or norepinephrine was reversed by propranolol. In addition, the slowing effect of fat was reversed by metoprolol (beta1-adrenoreceptor antagonist) but not phentolamine (alpha-adrenoreceptor antagonist). Furthermore, norepinephrine-induced slowing of transit was reversed by ondansetron (5-HT3 receptor antagonist) or naloxone (opioid receptor antagonist). Extending these physiological results, we also found by immunohistochemistry that beta1-adrenoreceptors are expressed by neurons of the intrinsic plexuses of the small intestine. We conclude that the slowing of intestinal transit by fat or PYY depends on a beta-adrenergic pathway and that this adrenergic pathway acts on serotonergic and opioid pathways.

Influence of bilirubin and other antioxidants on nitrergic relaxation in the pig gastric fundus

1. The influence of several antioxidants (bilirubin, urate, ascorbate, alpha-tocopherol, glutathione (GSH), Cu/Zn superoxide dismutase (SOD) and the manganese SOD mimic EUK-8) on nitrergic relaxations induced by either exogenous nitric oxide (NO; 10(-5) M) or electrical field stimulation (4 Hz; 10 s and 3 min) was studied in the pig gastric fundus. 2. Ascorbate (5x10(-4) M), alpha-tocopherol (4x10(-4) M), SOD (300 - 1000 u ml(-1)) and EUK-8 (3x10(-4) M) did not influence the relaxations to exogenous NO. In the presence of GSH (5x10(-4) M), the short-lasting relaxation to NO became biphasic, potentiated and prolonged. Urate (4x10(-4) M) and bilirubin (2x10(-4) M) also potentiated the relaxant effect of NO. None of the antioxidants influenced the electrically evoked relaxations. 3. 6-Anilino-5,8-quinolinedione (LY83583; 10(-5) M) had no influence on nitrergic nerve stimulation but nearly abolished the relaxant response to exogenous NO. Urate and GSH completely prevented this inhibitory effect, while it was partially reversed by SOD and bilirubin. Ascorbate, alpha-tocopherol and EUK-8 were without effect. 4. Hydroquinone (10(-4) M) did not affect the electrically induced nitrergic relaxations, but markedly reduced NO-induced relaxations. The inhibition of exogenous NO by hydroquinone was completely prevented by urate and GSH. SOD and ascorbate afforded partial protection, while bilirubin, EUK-8 and alpha-tocopherol were ineffective. 5. Hydroxocobalamin (10(-4) M) inhibited relaxations to NO by 50%, but not the electrically induced responses. Full protection versus this inhibitory effect was obtained with urate, GSH and alpha-tocopherol. 6. These results strengthen the hypothesis that several endogenous antioxidant defense mechanisms, enzymatic as well as non-enzymatic, might play a role in the nitrergic neurotransmission process.

Effects of superoxide anion generators and thiol modulators on nitrergic transmission and relaxation to exogenous nitric oxide in the sheep urethra

The effects of superoxide anion generators, the nitric oxide (NO) scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoine-1-oxyl 3-oxide (carboxy-PTIO), the specific guanylate cyclase inhibitor 1H-[1,2,4]-oxadiazole-[4,3-a]-quinoxalin-1-one (ODQ), and thiol modulating agents were investigated on relaxations induced by nitrergic stimulation and exogenous NO addition in the sheep urethra. Methylene blue (MB, 10 microM), pyrogallol (0.1 mM) and xanthine (X, 0.1 mM)/xanthine oxidase (XO, 0.1 u ml(-1)) inhibited NO-mediated relaxations, without affecting those induced by nitrergic stimulation. This resistance was not diminished following inhibition of endogenous Cu/Zn superoxide dismutase (Cu/Zn SOD) with diethyldithiocarbamic acid (DETCA, 3 mM), which almost abolished tissue SOD activity. Carboxy-PTIO (0.1 - 0.5 mM) inhibited NO-mediated relaxations but had no effect on responses to nitrergic stimulation, which were not changed by treatment with ascorbate oxidase (2 u ml(-1)). Relaxations to NO were reduced, but not abolished, by ODQ (10 microM), while nitrergic responses were completely blocked. The thiol modulators, ethacrynic acid (0.1 mM), diamide (1.5 mM), or 5,5'-dithio-bis (2-nitrobenzoic acid) (DTNB, 0. 5 mM), and subsequent treatment with dithiothreitol (DTT, 2 mM) had no effect on responses to nitrergic stimulation or NO. In contrast, N-ethylmaleimide (NEM, 0.2 mM) markedly inhibited both relaxations. L-cysteine (L-cys, 0.1 mM) had no effect on responses to NO, while it inhibited those to nitrergic stimulation, in a Cu/Zn SOD-independent manner. Our results do not support the view that the urethral nitrergic transmitter is free NO, and the possibility that another compound is acting as mediator still remains open. British Journal of Pharmacology (2000) 129, 53 - 62

Effect of thiol modulators and Cu/Zn superoxide dismutase inhibition on nitrergic relaxations in the rat gastric fundus

1. The effects of superoxide anion generators before and after treatment with inhibitors of Cu/Zn superoxide dismutase (Cu/Zn SOD) and the effects of thiol-modulating agents were investigated on nitrergic relaxations to electrical stimulation of non-adrenergic non-cholinergic (NANC) nerves of the rat gastric fundus and on relaxations to authentic nitric oxide (NO) and nitroglycerin. 2. The superoxide anion generators, pyrogallol (30 microM) and duroquinone (30-60 microM), significantly inhibited the relaxations to NO (0.03-3 microM) but not nitrergic relaxations to NANC nerve stimulation (0.5-8 Hz) or those to ATP (10 microM). Treatment of the rat gastric fundus with the inhibitors of Cu/Zn SOD, diethyldithiocarbamate (DETC, 1 mM for 2 h) or triethylenetetramine (TETA, 100 microM for 2 h) had no effect on the relaxations to NANC nerve stimulation (1-8 Hz), NO (0.03-3 microM) or on those to ATP (10 microM). 3. After treatment of the rat gastric fundus with DETC (1 mM) but not after treatment with TETA (100 microM), pyrogallol (30 microM) and duroquinone (30-60 microM) significantly inhibited the nitrergic relaxations to electrical stimulation (0.5-8 Hz) and those to NO (0.03-3 microM). This inhibitory effect of pyrogallol and duroquinone was prevented by addition of exogenous SOD (250 units ml-1). Pyrogallol but not duroquinone also inhibited the NO-independent relaxations to ATP (10 microM). 4. The thiol modulators, buthionine sulphoximine (1 mM for 2 h) and ethacrynic acid (30 microM for 2 h), significantly inhibited the relaxations to nitroglycerin (0.03-3 microM) but had no effect on the nitrergic relaxations to electrical stimulation (0.5-8 Hz) or on those to NO (0.03-10 microM) and ATP (10 microM). The thiol modulators, sulphobromophthalein (100 microM for 2 h) and diamide (30-100 microM for 2 h) did not affect the relaxations to nitroglycerin, or those to NANC nerve stimulation and NO. 5. In summary, thiol modulators significantly inhibited the thiol-dependent relaxations to nitroglycerin but not those to NANC nerve stimulation or NO. Relaxations to nitrergic stimulation were decreased by superoxide anion generators only after inhibition of Cu/Zn SOD. These results suggest that the nitrergic NANC neurotransmitter in the rat gastric fundus is not a nitrosothiol but more likely free NO, which is protected from breakdown by tissue SOD.