Roles of NADPH oxidase in occurrence of gastric damage and expression of cyclooxygenase-2 during ischemia/reperfusion in rat stomachs

Antidotal Potency of the Novel, Structurally Different Adsorbents in Rats Acutely Intoxicated with the T-2 Toxin

In this paper, the potential antidote efficacy of commercially available formulations of various feed additives such as Minazel-Plus^®, Mycosorb^®, and Mycofix^® was considered by recording their incidence on general health, body weight, and food and water intake, as well as through histopathology and semiquantitative analysis of gastric alterations in Wistar rats treated with the T-2 toxin in a single-dose regimen of 1.67 mg/kg p.o. (1 LD₅₀) for 4 weeks. As an organic adsorbent, Mycosorb^® successfully antagonized acute lethal incidence of the T-2 toxin (protective index (PI) = 2.25; p < 0.05 vs. T-2 toxin), and had adverse effects on body weight gain as well as food and water intake during the research (p < 0.001). However, the protective efficacy of the other two food additives was significantly lower (p < 0.05). Treatment with Mycosorb^® significantly reduced the severity of gastric damage, which was not the case when the other two adsorbents were used. Our results suggest that Mycosorb^® is a much better adsorbent for preventing the adverse impact of the T-2 toxin as well as its toxic metabolites compared with Minazel-plus^® or Mycofix-plus^®, and it almost completely suppresses its acute toxic effects and cytotoxic potential on the gastric epithelial, glandular, and vascular endothelial cells.

Prevention of stress-related ulcer bleeding at the intensive care unit: Risks and benefits of stress ulcer prophylaxis

Stress-related mucosal disease is a typical complication of critically ill patients in the intensive care unit (ICU). It poses a risk of clinically relevant upper gastrointestinal (GI) bleeding. Therefore, stress ulcer prophylaxis (SUP) is recommended in high-risk patients, especially those mechanically ventilated > 48 h and those with a manifest coagulopathy. Proton pump inhibitors (PPI) and, less effectively, histamine 2 receptor antagonists (H2RA) prevent GI bleeding in critically ill patients in the ICU. However, the routine use of pharmacological SUP does not reduce overall mortality in ICU patients. Moreover, recent studies revealed that SUP in the ICU might be associated with potential harm such as an increased risk of infectious complications, especially nosocomial pneumonia and Clostridium difficile-associated diarrhea. Additionally, special populations such as patients with liver cirrhosis may even have an increased mortality rate if treated with PPI. Likewise, PPI can be toxic for both the liver and the bone marrow, and some PPI show clinically relevant interactions with important other drugs like clopidogrel. Therefore, the agent of choice, the specific balance of risks and benefits for individual patients as well as the possible dose of PPI has to be chosen carefully. Alternatives to PPI prophylaxis include H2RA and/or sucralfate. Instead of routine SUP, further trials should investigate risk-adjusted algorithms, balancing benefits and threats of SUP medication in the ICU.

Physiological role of taurine--from organism to organelle

Taurine is often referred to as a semi-essential amino acid as newborn mammals have a limited ability to synthesize taurine and have to rely on dietary supply. Taurine is not thought to be incorporated into proteins as no aminoacyl tRNA synthetase has yet been identified and is not oxidized in mammalian cells. However, taurine contributes significantly to the cellular pool of organic osmolytes and has accordingly been acknowledged for its role in cell volume restoration following osmotic perturbation. This review describes taurine homeostasis in cells and organelles with emphasis on taurine biophysics/membrane dynamics, regulation of transport proteins involved in active taurine uptake and passive taurine release as well as physiological processes, for example, development, lung function, mitochondrial function, antioxidative defence and apoptosis which seem to be affected by a shift in the expression of the taurine transporters and/or the cellular taurine content.

ROS dependence of cyclooxygenase-2 induction in rats subjected to unilateral ureteral obstruction

Oxidative stress resulting from unilateral ureteral obstruction (UUO) may be aggravated by increased production of ROS. Previous studies have demonstrated increased cyclooxygenase (COX)-2 expression in renal medullary interstitial cells (RMICs) in response to UUO. We investigated, both in vivo and in vitro, the role of ROS in the induction of COX-2 in rats subjected to UUO and in RMICs exposed to oxidative and mechanical stress. Rats subjected to 3-day UUO were treated with two mechanistically distinct antioxidants, the NADPH oxidase inhibitor diphenyleneiodonium (DPI) and the complex I inhibitor rotenone (ROT), to interfere with ROS production. We found that UUO-mediated induction of COX-2 in the inner medulla was attenuated by both antioxidants. In addition, DPI and ROT reduced tubular damage and oxidative stress after UUO. Moreover, mechanical stretch induced COX-2 and oxidative stress in RMICs. Likewise, RMICs exposed to H2O2 as an inducer of oxidative stress showed increased COX-2 expression and activity, both of which were reduced by DPI and ROT. Similarly, ROS production, which was increased after exposure of RMICs to H2O2, was also reduced by DPI and ROT. Furthermore, oxidative stress-induced phosphorylation of ERK1/2 and p38 was blocked by both antioxidants, and inhibition of ERK1/2 and p38 attenuated the induction of COX-2 in RMICs. Notably, COX-2 inhibitors further exacerbated the oxidative stress level in H2O2-exposed RMICs. We conclude that oxidative stress as a consequence of UUO stimulates COX-2 expression through the activation of multiple MAPKs and that the induction of COX-2 may exert a cytoprotective function in RMICs.

Protective effect of 3,4-methylenedioxyphenol (sesamol) on stress-related mucosal disease in rats

Stress-related mucosal disease (SRMD) causes considerable morbidity and mortality in critically ill patients. 3,4-Methylenedioxyphenol (sesamol) has been reported to have potent antioxidative and anti-inflammatory properties. The aim of this study was to investigate the effect of sesamol on water immersion restraint- (WIR-) induced SRMD in rats. Rat gastric ulcer and hemorrhage were induced by WIR. Rats were pretreated orally with various doses of sesamol (0.1, 0.3, and 1 mg/kg, resp.) 30 min before WIR. Gastric mucosal ulceration, hemoglobin, lipid peroxidation, mucus secretion, proinflammatory cytokines, and nuclear factor (NF)-κB levels were determined 4 h after WIR. In addition, the infiltration of neutrophil and macrophage into gastric mucosa was also determined after WIR. Water immersion restraint increased gastric mucosal ulcer and hemorrhage, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 levels but failed to affect mucosal lipid peroxidation and mucus secretion compared with non-WIR. Sesamol significantly decreased gastric ulceration and hemorrhage and inhibited mucosal TNF-α, IL-1β, and IL-6 production and NF-κB activity in WIR-treated rats. In addition, increased myeloperoxidase and CD68 levels in gastric mucosa were found in WIR-treated rats compared to non-WIR rats. Sesamol did not affect myeloperoxidase but decreased CD68 levels in mucosa in WIR-treated rats. Sesamol may protect against SRMD by inhibiting gastric mucosal proinflammatory cytokines in rats.

Volume-sensitive release of organic osmolytes in the human lung epithelial cell line A549: role of the 5-lipoxygenase

Pathophysiological conditions challenge cell volume homeostasis and perturb cell volume regulatory mechanisms leading to alterations of cell metabolism, active transepithelial transport, cell migration, and death. We report that inhibition of the 5-lipoxygenase (5-LO) with AA861 or ETH 615-139, the cysteinyl leukotriene 1 receptor (CysLT₁) with the antiasthmatic drug Zafirlukast, or the volume-sensitive organic anion channel (VSOAC) with DIDS blocks the release of organic osmolytes (taurine, meAIB) and the concomitant cell volume restoration following hypoosmotic swelling of human type II-like lung epithelial cells (A549). Reactive oxygen species (ROS) are produced in A549 cells upon hypotonic cell swelling by a diphenylene iodonium-sensitive NADPH oxidase. The swelling-induced taurine release is suppressed by ROS scavenging (butylated hydroxytoluene, N-acetyl cysteine) and potentiated by H₂O₂. Ca²⁺ mobilization with ionomycin or ATP stimulates the swelling-induced taurine release whereas calmodulin inhibition (W7) inhibits the release. Chelation of the extracellular Ca²⁺ (EGTA) had no effect on swelling-induced taurine release but prevented ATP-induced stimulation. H₂O₂, ATP, and ionomycin were unable to stimulate the taurine release in the presence of AA861 or Zafirlukast, placing 5-LO and CysLT₁ as essential elements in the swelling-induced activation of VSOAC with ROS and Ca²⁺ as potent modulators. Inhibition of tyrosine kinases (genistein, cucurbitacin) reduces volume-sensitive taurine release, adding tyrosine kinases (Janus kinase) as regulators of VSOAC activity. Caspase-3 activity during hypoxia is unaffected by inhibition of 5-LO/CysLT₁ but reduced when swelling-induced taurine loss via VSOAC is prevented by DIDS excess extracellular taurine, indicating a beneficial role of taurine under hypoxia.

Tangeretin reduces ultraviolet B (UVB)-induced cyclooxygenase-2 expression in mouse epidermal cells by blocking mitogen-activated protein kinase (MAPK) activation and reactive oxygen species (ROS) generation

The present study examined the effects of tangeretin, a polymethoxylated flavonone present in citrus fruits, on ultraviolet B (UVB)-induced cyclooxygenase-2 (COX-2) expression in JB6 P+ mouse skin epidermal cells. Tangeretin suppressed UVB-induced COX-2 expression and transactivation of nuclear factor-κB and activator protein-1 in JB6 P+ cells. Moreover, tangeretin blocked UVB-induced phosphorylation of Akt and mitogen-activated protein kinases (MAPKs), including extracellular signal-regulated protein kinase, c-Jun N-terminal kinase, and p38, and attenuated the phosphorylation of MAPK kinases 1/2, 3/6, and 4. Tangeretin also limited the endogenous generation of reactive oxygen species (ROS), thereby protecting the cells against oxidative stress. However, tangeretin did not scavenge the stable 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and influence the nicotinamide adenine dinucleotide phosphate oxidase activity. These results suggest that the anti-inflammatory effects of tangeretin stem from its modulation of cell signaling and suppression of intracellular ROS generation. Tangeretin may have a potent chemopreventive effect in skin cancer.

Gastroduodenal mucosal defense

PURPOSE OF REVIEW

We have summarized recent findings related to gastroduodenal mucosal defense as well as factors contributing to defensive failure, highlighting findings that illuminate new pathophysiological mechanisms.

RECENT FINDINGS

Gastroduodenal bicarbonate secretion is mediated by prostaglandin E receptors and stimulated by the prostone lubiprostone. Toll-like receptor (TLR)4 signaling is protective against gastric injury. Intestinal alkaline phosphatase (IAP) is a chemosensor that regulates the duodenal mucosal surface pH. Lipopolysaccharide (LPS) increases gastric permeability; IAP secreted during fat digestion may detoxify colonic LPS. NADPH oxidase activity mediates ischemia/reperfusion-related gastric mucosal damage. Heat shock protein 70 (HSP70) protects the gastric mucosa through inhibition of apoptosis, proinflammatory cytokines, and cell adhesion molecules (CAMs). HSP90 may be a contributing factor in impaired adaptive cytoprotection. Proteinase-activated receptor-1 (PAR-1) is protective against Helicobacter-induced gastritis, mediated by the suppression of proinflammatory pathways. IKK β/NF-κB signaling decreases chronic Helicobacter-induced inflammation by inhibiting cellular apoptosis and necrosis. Activation of A2A adenosine receptors decreases inflammation and gastritis but leads to persistent Helicobacter pylori infection.

SUMMARY

Enhanced understanding of the mechanisms of gastroduodenal defense and injury provides new insight into potential therapeutic targets, contributing towards the development of better tolerated and more effective therapies.