Effect of orexin-a on ischemia-reperfusion-induced gastric damage in rats

Inclusion of hypocretin-1 improved performance of poor sleep quality prediction for elderly patients with acute ischemic stroke: a prospective cohort study

Background

Hypocretin-1 is a vital neurotransmitter in regulating the sleep-wake cycle and provides neuroprotection against cerebral ischemia. We aims to develop a poor sleep quality predictive model for elderly population with acute ischemic stroke.

Methods

A total of 183 consecutively elderly patients were included in the prospective cohort study. Sleep quality was assessed by the Pittsburgh Sleep Quality Index (PSQI). Cerebrospinal fluid samples were taken within 24 h of acute ischemic stroke onset. After selecting optimal predictors via univariate analysis and bootstrapped stepwise logistic regression, the predictive model was developed. The models were internally validated and evaluated comprehensively via discrimination, calibration, and clinical utility.

Results

The prevalence of poor sleep (PSQI >7) was 64.5% among elderly individuals experiencing acute ischemic stroke. The study developed a predictive model using hypocretin-1, hypertension, stroke history, the National Institutes of Health Stroke score, and depression. Adding hypocretin-1 (as continuous variable) significantly improved the model performance greatly, as the area under the receiver operating characteristic curve increased from 0.799 to 0.845 (p < 0.001). The optimal cutoff value for hypocretin-1 was 74.94 pg/mL. Adding hypocretin-1 (as binary variable) significantly improved the model performance greatly, as the AUC increased from 0.799 to 0.857 (p < 0.001).

Conclusion

Reduced cerebrospinal fluid levels of hypocretin-1 at admission were an independent poor sleep quality predictor and the model demonstrated superior performance. The combination of hypocretin-1 could offer valuable prognostic information for post-stroke sleep quality in elderly patients with acute ischemic stroke.

Bioelectric, tissue, and molecular characteristics of the gastric mucosa at different times of ischemia

Gastrointestinal ischemia may be presented as a complication associated with late shock detection in patients in critical condition. Prolonged ischemia can cause mucosal integrity to lose its barrier function, triggering alterations that can induce organ dysfunction and lead to death. Electrical impedance spectroscopy has been proposed to identify early alteration in ischemia-induced gastric mucosa in this type of patients. This work analyzed changes in impedance parameters, and tissue and molecular alterations that allow us to identify the time of ischemia in which the gastric mucosa still maintains its barrier function. The animals were randomly distributed in four groups: Control, Ischemia 60, 90, and 120 min. Impedance parameters were measured and predictive values were determined to categorize the degree of injury using a receiver operating characteristic curve. Markers of inflammatory process and apoptosis (iNOS, TNFα, COX-2, and Caspase-3) were analyzed. The largest increase in impedance parameters occurred in the ischemia 90 and 120 min groups, with resistance at low frequencies (RL) and reactance at high frequencies (XH) being the most related to damage, allowing prediction of the occurrence of reversible and irreversible tissue damage. Histological analysis and apoptosis assay showed progressive mucosal deterioration with irreversible damage (p < 0.001) starting from 90 min of ischemia. Furthermore, a significant increase in the expression of iNOS, TNFα, and COX-2 was identified in addition to apoptosis in the gastric mucosa starting from 90 min of ischemia. Tissue damage generated by an ischemia time greater than 60 min induces loss of barrier function in the gastric mucosa.

Orexin-A alleviates astrocytic apoptosis and inflammation via inhibiting OX1R-mediated NF-κB and MAPK signaling pathways in cerebral ischemia/reperfusion injury

Orexin-A (OXA) is a neuropeptide with neuroprotective effect by reducing cerebral ischemia/reperfusion injury (CIRI). Inflammation and apoptosis mediated by astrocyte activation are the key pathological mechanisms for CIRI. We thus attempted to confirm neuroprotective effects of OXA on astrocytic inflammation and apoptosis in CIRI and clarify the relative mechanisms. A middle cerebral artery occlusion and reperfusion (MCAO/R) rat model and U251 glioma cells model subjected to oxygen glucose deprivation and reperfusion (OGD/R) were established, with or without OXA treatment. Neurological deficit score was determined, and cerebral infarct volume was evaluated by 2,3,5-triphenyltetrazolium chloride (TTC) staining. Western Blot was used to detect the expressions of NF-κB p65, p-p65, p-ERK, p-p38, GFAP, OX1R, IL-1β, TNF-α, IL-6, iNOS, Bcl-2, Bax, CytC, cleaved caspase-9 and cleaved caspase-3 in vivo and in vitro. Pro-inflammatory cytokines in cell supernatant IL-1β, TNF-α and IL-6 were determined by ELISA. Hoechst 33342 staining was used to detect the apoptosis of astrocyte. Immunofluorescent staining was performed to assess the nuclear translocation of p65 and the expression of GFAP. The results showed that OXA significantly improved neurological deficit score and decreased the volume of infarct area in brain. OXA decreased inflammatory mediators, inhibited astrocyte activation and nuclear translocation of NF-κB and phosphorylation of NF-κB, MAPK/ERK and MAPK/p38. Besides, OXA suppressed apoptosis via upregulating the ratio of Bcl-2/Bax and downregulating cytochrome C, cleaved-caspase-9 and cleaved caspase-3. Overall, it was concluded that OXA exerts neuroprotective effect during CIRI through attenuating astrocytes apoptosis, astrocytes activation and pro-inflammatory cytokines production, by Inhibiting OX1R-mediated NF-κB, MAPK/ERK and MAPK/p38 signaling pathways. The progress in our study is helpful to elucidate the molecular mechanisms of OXA neuroprotection, which could lead to the development of new treatment strategies for ischemic stroke.

Orexin A improves the cognitive impairment induced by chronic intermittent hypoxia in mice

The orexin neuron in lateral hypothalamus (LH) was involved in the regulation of sleep-wake cycle. However, the effect of orexin A (OXA) on cognitive impairment resulting from diverse diseases remains controversial. In this study, we investigated the effect of OXA on cognitive impairment induced by chronic intermittent hypoxia (CIH) in mice. Adult (10 weeks old) male C57BL/6 mice were randomly divided into the following four groups: normoxia control (NC)+normal saline (NS), NC + OXA, CIH + NS and CIH + OXA group. Following the CIH mice models establishment, OXA was injected into the right lateral ventricles of mice by a micro-injection system. Water maze test was used to assess spatial memory abilities of the mice. The expression of OXA and c-Fos in LH were analyzed by immunofluorescence staining. Apoptotic cell death and oxidative stress in hippocampus were evaluated using multiple methods including TUNEL, western blot and biochemical analysis. Behavioral tests revealed that CIH significantly increased the escape latency and time of arriving platform, of which were markedly decreased by OXA treatment. Similarly, the CIH + NS group was worse than NC + NS group in terms of the number of platform crossing and time in the target quadrant, of which were also significantly improved by OXA treatment. The number of OXA + neuron in LH was decreased, but the percentage of c-Fos+/OXA + neuron in LH was remarkably increased by CIH. Furthermore, we found that micro-injection of OXA attenuated CIH-induced apoptotic cell death and oxidative stress in the hippocampus. Our results suggested that OXA might improve cognitive impairment induced by CIH through inhibiting hippocampal apoptosis and oxidative stress.

Intranasal insulin and orexins to treat age-related cognitive decline

The intranasal (IN) administration of neuropeptides, such as insulin and orexins, has been suggested as a treatment strategy for age-related cognitive decline (ARCD). Because dysfunctional neuropeptide signaling is an observed characteristic of ARCD, it has been suggested that IN delivery of insulin and/or orexins may restore endogenous peptide signaling and thereby preserve cognition. IN administration is particularly alluring as it is a relatively non-invasive method that directly targets peptides to the brain. Several laboratories have examined the behavioral effects of IN insulin in young, aged, and cognitively impaired rodents and humans. These studies demonstrated improved performance on various cognitive tasks following IN insulin administration. Fewer laboratories have assessed the effects of IN orexins; however, this peptide also holds promise as an effective treatment for ARCD through the activation of the cholinergic system and/or the reduction of neuroinflammation. Here, we provide a brief overview of the advantages of IN administration and the delivery pathway, then summarize the current literature on IN insulin and orexins. Additional preclinical studies will be useful to ultimately uncover the mechanisms underlying the pro-cognitive effects of IN insulin and orexins, whereas future clinical studies will aid in the determination of the most efficacious dose and dosing paradigm. Eventually, IN insulin and/or orexin administration may be a widely used treatment strategy in the clinic for ARCD.

Orexin-A protects against cerebral ischemia-reperfusion injury by inhibiting excessive autophagy through OX1R-mediated MAPK/ERK/mTOR pathway

Orexin A (OXA) is a neuroprotective peptide that exerts protective effects on multiple physiological and pathological processes. Activation of autophagy is linked to the occurrence of cerebral ischemia-reperfusion injury (CIRI); however, its function remains incompletely understood. In this study, OXA was sought to exert its neuroprotective role by regulating autophagy in oxygen and glucose deprivation and reoxygenation (OGD/R) model and middle cerebral artery occlusion (MCAO) model of rats, and to elucidate the underlying molecular mechanisms. Acridine orange (AO) staining was used to evaluate autophagic vacuoles. Cell viability was measured by CCK8. The levels of p-ERK_1/2, t-ERK_1/2, p-mTOR, LC3B, Beclin 1, and p62 were evaluated by western blotting. Apoptosis rate was detected by Hoechst 33342 staining and Terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling (TUNEL). OXA treatment alleviated neuronal apoptosis and significantly inhibited autophagy activity. Mechanistically, OXA exerted its neuroprotective effects in vivo and in vitro by suppressing over-activated autophagy by modulating OX1R-mediated MAPK/ERK/mTOR pathway. The results of this study elucidate the roles of autophagy in CIRI and the mechanisms underlying the neuroprotective action of OXA. Our findings could facilitate the development of novel therapeutics for ischemic stroke.

Role of 2-Arachidonoyl-Glycerol and CB1 Receptors in Orexin-A-Mediated Prevention of Oxygen-Glucose Deprivation-Induced Neuronal Injury

Orexin-A (OX-A) protects the brain against oxidative stress-mediated ischemic injury. Since the endocannabinoid 2-arachidonoylglycerol (2-AG) and cannabinoid type-1 (CB1) receptors were previously shown to mediate some of the effects of OX-A exerted through the orexin-1 receptor (OX-1R), we investigated the involvement of 2-AG in OX-A-induced neuroprotection following oxygen and glucose deprivation (OGD) in mouse cortical neurons. OGD-induced reactive oxygen species (ROS) accumulation and neuronal death were prevented by both OX-A and arachidonyl-2′-chloroethylamide (ACEA), a synthetic CB1 receptor agonist, in a manner sensitive to OX-1R and CB1 receptor antagonists, SB334867 and AM251. OX-A stimulated 2-AG biosynthesis in cortical neurons. In neurons isolated from monoacylglycerol lipase (MAGL, a 2-AG hydrolyzing enzyme) null mice, 10-fold higher 2-AG concentrations were found and OGD failed to induce ROS production and cell death, whereas AM251 restored these noxious effects. OX-A-induced neuroprotection was mediated by the phosphoinositide-3-kinase/Akt (PI3K/Akt) survival pathway since both OX-A and ACEA induced phosphorylation of Akt and prevented OGD-induced cytochrome c release from the mitochondria, in a manner counteracted by SB334867 or AM251. Administration of OX-A reduced infarct volume and elevated brain 2-AG levels in a mouse model of transient ischemia. These results suggest that 2-AG and CB1 receptor mediate OX-A prevention of ischemia-induced neuronal apoptosis.

Orexins as Novel Therapeutic Targets in Inflammatory and Neurodegenerative Diseases

Orexins [orexin-A (OXA) and orexin-B (OXB)] are two isoforms of neuropeptides produced by the hypothalamus. The main biological actions of orexins, focused on the central nervous system, are to control the sleep/wake process, appetite and feeding, energy homeostasis, drug addiction, and cognitive processes. These effects are mediated by two G protein-coupled receptor (GPCR) subtypes named OX1R and OX2R. In accordance with the synergic and dynamic relationship between the nervous and immune systems, orexins also have neuroprotective and immuno-regulatory (i.e., anti-inflammatory) properties. The present review gathers recent data demonstrating that orexins may have a therapeutic potential in several pathologies with an immune component including multiple sclerosis, Alzheimer's disease, narcolepsy, obesity, intestinal bowel diseases, septic shock, and cancers.

Protective roles of bioactive peptides during ischemia-reperfusion injury: From bench to bedside

Ischemia-reperfusion (I/R) is a well-known pathological condition which may lead to disability and mortality. I/R injury remains an unresolved and complicated situation in a number of clinical conditions, such as cardiac arrest with successful reanimation, as well as ischemic events in brain and heart. Peptides have many attractive advantages which make them suitable candidate drugs in treating I/R injury, such as low toxicity and immunogenicity, good solubility property, distinct tissue distribution pattern, and favorable pharmacokinetic profile. An increasing number of studies indicate that peptides could protect against I/R injury in many different organs and tissues. Peptides also face several therapeutic challenges that limit their clinical application. In this review, we present the mechanisms of action of peptides in reducing I/R injury, as well as further discuss modification strategies to improve the functional properties of bioactive peptides.

Orexin A attenuates palmitic acid-induced hypothalamic cell death

Palmitic acid (PA), an abundant dietary saturated fatty acid, contributes to obesity and hypothalamic dysregulation in part through increase in oxidative stress, insulin resistance, and neuroinflammation. Increased production of reactive oxygen species (ROS) as a result of PA exposure contributes to the onset of neuronal apoptosis. Additionally, high fat diets lead to changes in hypothalamic gene expression profiles including suppression of the anti-apoptotic protein B cell lymphoma 2 (Bcl-2) and upregulation of the pro-apoptotic protein B cell lymphoma 2 associated X protein (Bax). Orexin A (OXA), a hypothalamic peptide important in obesity resistance, also contributes to neuroprotection. Prior studies have demonstrated that OXA attenuates oxidative stress induced cell death. We hypothesized that OXA would be neuroprotective against PA induced cell death. To test this, we treated an immortalized hypothalamic cell line (designated mHypoA-1/2) with OXA and PA. We demonstrate that OXA attenuates PA-induced hypothalamic cell death via reduced caspase-3/7 apoptosis, stabilization of Bcl-2 gene expression, and reduced Bax/Bcl-2 gene expression ratio. We also found that OXA inhibits ROS production after PA exposure. Finally, we show that PA exposure in mHypoA-1/2 cells significantly reduces basal respiration, maximum respiration, ATP production, and reserve capacity. However, OXA treatment reverses PA-induced changes in intracellular metabolism, increasing basal respiration, maximum respiration, ATP production, and reserve capacity. Collectively, these results support that OXA protects against PA-induced hypothalamic dysregulation, and may represent one mechanism through which OXA can ameliorate effects of obesogenic diet on brain health.

Role of orexin-A in experimental autoimmune encephalomyelitis

The aim of this study was to evaluate the effects of orexin-A (OX-A) on behavioral and pathological parameters and on gene expression of some multiple sclerosis-related peptides in a model of experimental autoimmune encephalomyelitis (EAE). EAE was induced by subcutaneous administration of MOG 35-55. Following immunization, the treatment was initiated by using SB.334867 (orexin-1 receptor antagonist) and/or OX-A. Locomotor activity and exploratory behaviors were monitored using open field and T-maze continuous alternation task (T-CAT) respectively. Pain sensitivity was assessed by hot-plate test. Histopathological assessments were performed by H&E staining. The expression of TGF-β, MBP, MMP-9, IL-12, iNOS and MCP-1 were measured using real-time PCR method in lumbar spinal cord. OX-A administration in EAE mice remarkably attenuated the clinical symptoms, increased latency response in hot plate test, inhibited infiltration of inflammatory cells, up-regulated mRNA expression of TGF-β as well as MBP and down-regulated mRNA expression of iNOS, MMP-9 and IL-12. In contrast SB.334867 administration in EAE mice deteriorated the clinical symptoms, decreased the alternation in T-CAT, increased infiltration of inflammatory cells, down-regulated mRNA expression of TGF-β and MBP and up-regulated mRNA expression of iNOS. Results of this study suggest that the orexinergic system might be involved in pathological development of EAE. These findings suggest orexinergic system as a potential target for treatment of multiple sclerosis.

Gaseous mediators nitric oxide and hydrogen sulfide in the mechanism of gastrointestinal integrity, protection and ulcer healing

Nitric oxide (NO) and hydrogen sulfide (H2S) are known as biological messengers; they play an important role in human organism and contribute to many physiological and pathophysiological processes. NO is produced from l-arginine by constitutive NO synthase (NOS) and inducible NOS enzymatic pathways. This gaseous mediator inhibits platelet aggregation, leukocyte adhesion and contributes to the vessel homeostasis. NO is known as a vasodilatory molecule involved in control of the gastric blood flow (GBF) and the maintenance of gastric mucosal barrier integrity in either healthy gastric mucosa or that damaged by strong irritants. Biosynthesis of H2S in mammals depends upon two enzymes cystathionine-β-synthase and cystathionine γ-lyase. This gaseous mediator, similarly to NO and carbon monoxide, is involved in neuromodulation, vascular contractility and anti-inflammatory activities. For decades, H2S has been known to inhibit cytochrome c oxidase and reduce cell energy production. Nowadays it is generally considered to act through vascular smooth muscle ATP-dependent K+ channels, interacting with intracellular transcription factors and promote sulfhydration of protein cysteine moieties within the cell, but the mechanism of potential gastroprotective and ulcer healing properties of H2S has not been fully explained. The aim of this review is to compare current results of the studies concerning the role of H2S and NO in gastric mucosa protection and outline areas that may pose new opportunities for further development of novel therapeutic targets.

The role of orexin in post-stroke inflammation, cognitive decline, and depression

Ischemic stroke results in diverse pathophysiologies, including cerebral inflammation, neuronal loss, cognitive dysfunction, and depression. Studies aimed at identifying therapeutic solutions to alleviate these outcomes are important due to the increase in the number of stroke patients annually. Recently, many studies have reported that orexin, commonly known as a neuropeptide regulator of sleep/wakefulness and appetite, is associated with neuronal cell apoptosis, memory function, and depressive symptoms. Here, we briefly summarize recent studies regarding the role and future perspectives of orexin in post-ischemic stroke. This review advances our understanding of the role of orexin in post-stroke pathologies, focusing on its possible function as a therapeutic regulator in the post-ischemic brain. Ultimately, we suggest the clinical potential of orexin to regulate post-stroke pathologies.

The hypocretins/orexins: integrators of multiple physiological functions

The hypocretins (Hcrts), also known as orexins, are two peptides derived from a single precursor produced in the posterior lateral hypothalamus. Over the past decade, the orexin system has been associated with numerous physiological functions, including sleep/arousal, energy homeostasis, endocrine, visceral functions and pathological states, such as narcolepsy and drug abuse. Here, we review the discovery of Hcrt/orexins and their receptors and propose a hypothesis as to how the orexin system orchestrates these multifaceted physiological functions.

Mitigation of murine focal cerebral ischemia by the hypocretin/orexin system is associated with reduced inflammation

BACKGROUND AND PURPOSE

Brain ischemia causes immediate and delayed cell death that is exacerbated by inflammation. Recent studies show that hypocretin-1/orexin-A (Hcrt-1) reduces ischemic brain injury, and Hcrt-positive neurons modulate infection-induced inflammation. Here, we tested the hypothesis that Hcrt plays a protective role against ischemia by modulating inflammation.

METHODS

Orexin/ataxin-3 (AT) mice, a transgenic strain in which Hcrt-producing neurons degenerate in early adulthood, and wild-type mice were subjected to transient middle cerebral artery occlusion (MCAO). Infarct volume, neurological score, and spontaneous home cage activity were assessed. Inflammation was measured using immunohistochemistry, ELISA, and assessment of cytokine mRNA levels.

RESULTS

Infarct volumes 24 and 48 hours after MCAO were significantly larger, neurological score was worse, and spontaneous activity decreased in AT compared with wild-type mice. Macrophage/microglial infiltration and myeloperoxidase-positive cells were higher in AT compared with wild-type mice. Pre-MCAO intracerebroventricular injection of Hcrt-1 significantly reduced infarct volume and macrophage/microglial infiltration in both genotypes and improved neurological score in AT mice. Post-MCAO treatment decreased infarct size in both wild-type and AT mice, but had no effect on neurological score in either genotype. Microglia express the Hcrt-1 receptor after MCAO. Tumor necrosis factor-α production by lipopolysaccharide-stimulated microglial BV2 cells was significantly reduced by Hcrt-1 pretreatment. Sham AT mice exhibit increased brain tumor necrosis factor-α and interleukin-6 mRNA, suggesting chronic inflammation.

CONCLUSIONS

Loss of Hcrt neurons in AT mice resulted in worsened stroke outcomes, which were reversed by administration of exogenous Hcrt-1. The mechanism underlying Hcrt-mediated neuroprotection includes attenuation of inflammatory responses after ischemic insult.

Orexin A decreases lipid peroxidation and apoptosis in a novel hypothalamic cell model

Current data support the idea that hypothalamic neuropeptide orexin A (OxA; hypocretin 1) mediates resistance to high fat diet-induced obesity. We previously demonstrated that OxA elevates spontaneous physical activity (SPA), that rodents with high SPA have higher endogenous orexin sensitivity, and that OxA-induced SPA contributes to obesity resistance in rodents. Recent reports show that OxA can confer neuroprotection against ischemic damage, and may decrease lipid peroxidation. This is noteworthy as independent lines of evidence indicate that diets high in saturated fats can decrease SPA, increase hypothalamic apoptosis, and lead to obesity. Together data suggest OxA may protect against obesity both by inducing SPA and by modulation of anti-apoptotic mechanisms. While OxA effects on SPA are well characterized, little is known about the short- and long-term effects of hypothalamic OxA signaling on intracellular neuronal metabolic status, or the physiological relevance of such signaling to SPA. To address this issue, we evaluated the neuroprotective effects of OxA in a novel immortalized primary embryonic rat hypothalamic cell line. We demonstrate for the first time that OxA increases cell viability during hydrogen peroxide challenge, decreases hydrogen peroxide-induced lipid peroxidative stress, and decreases caspase 3/7 induced apoptosis in an in vitro hypothalamic model. Our data support the hypothesis that OxA may promote obesity resistance both by increasing SPA, and by influencing survival of OxA-responsive hypothalamic neurons. Further identification of the individual mediators of the anti-apoptotic and peroxidative effects of OxA on target neurons could lead to therapies designed to maintain elevated SPA and increase obesity resistance.

Cellular and molecular mechanisms of 17beta-estradiol postconditioning protection against gastric mucosal injury induced by ischemia/reperfusion in rats

AIMS

To investigate the protective effects of 17beta-estradiol postconditioning against ischemia/reperfusion (I-R)-induced gastric mucosal injury in rats.

MAIN METHODS

The animal model of gastric ischemia/reperfusion was established by clamping of the celiac artery for 30 min and reperfusion for 30 min, 1h, 3h, 6h, 12h or 24h. 17beta-estradiol at doses of 5, 50 or 100 microg/kg (rat) was administered via peripheral veins 2 min before reperfusion. In a subgroup of rats, the estrogen receptor antagonist fulvestrant (Ful, 2mg/kg) was intravenously injected prior to 17beta-estradiol administration. Histological and immunohistochemical methods were employed to assess the gastric mucosal injury index and gastric mucosal cell apoptosis and proliferation. The malondialdehyde (MDA) concentration, superoxide dismutase (SOD) activity, xanthine oxidase (XOD) activity and hydroxyl free radical (-OH) inhibitory ability were determined by colorimetric assays. Subsequently, the expression of Bcl-2 and Bax in rat gastric mucosa was examined by western blotting.

KEY FINDINGS

17beta-estradiol dose-dependently inhibited gastric I-R (GI-R) injury, and 17beta-estradiol (50 microg/kg) markedly attenuated GI-R injury 1h after reperfusion. 17beta-estradiol inhibited gastric mucosal cell apoptosis and promoted gastric mucosal cell proliferation in addition to increasing SOD activity and -OH inhibitory ability and decreasing the MDA content and XOD activity. The Bax protein level increased 1h after GI-R and was markedly reduced by intravenous administration of 17beta-estradiol. In contrast, the level of Bcl-2 protein decreased 1h after GI-R and was restored to normal levels by intravenous administration of 17beta-estradiol. These effects of 17beta-estradiol were inhibited by pretreatment with fulvestrant.

SIGNIFICANCE

17beta-estradiol postconditioning should be investigated further as a possible strategy against gastric mucosal injury.

Gastroduodenal mucosal defense

PURPOSE OF REVIEW

The gastroduodenum has multiple means by which it resists injury from intrinsic and extrinsic factors, including gastric acid, nonsteroidal anti-inflammatory drugs, and Helicobacter pylori. We review recent insights into the mechanisms by which the gastroduodenum resists injury and discuss factors contributing to defensive failure.

RECENT FINDINGS

Duodenal bicarbonate secretion, a primary defensive mechanism, is mediated by the downregulated in adenoma anion exchanger and is stimulated by estrogens. Nonsteroidal anti-inflammatory drug gastric damage is dependent on toll-like receptor signaling. Portal hypertensive gastropathy impairs extracellular signal-regulated kinase 1/2 phosphorylation, increasing oxidative stress. H. pylori-induced peptic ulcer disease is associated with inadequate regulatory T cell responses.

SUMMARY

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

Gastroduodenal mucosal defense

The gastroduodenal mucosa withstands injury from acid, drugs, foodstuffs, and other factors. Defense mechanisms include pre-epithelial and epithelial barriers, submucosal acid sensors, prostaglandin generation, endogenous protective gases, and other chemical mediators. Recent studies have focused on proteinase-activated receptors and their linkage to prostaglandin formation, as well as on antioxidants targeted to reduce harmful reactive oxygen species. Investigation continues into the protective roles of calcitonin gene-related peptide, hydrogen sulfide, annexin-1, survivin, and methylnicotinamide. This article also summarizes some new findings on the genetics of ulcer formation and the effects of age and gender on mucosal defense and touches on current developments in drugs, including considerations for future therapeutic agents.