Na+/H+ exchanger blockade inhibits enterocyte inflammatory response and protects against colitis

The role of the Notch signalling pathway in the pathogenesis of ulcerative colitis: from the perspective of intestinal mucosal barrier

Ulcerative colitis is a common digestive disorder worldwide, with increasing incidence in recent years. It is an urgent problem to be solved, as it seriously affects and threatens the health and life of the global population. Studies have shown that dysfunction of the intestinal mucosal barrier is a critical pathogenic factor and molecular basis of ulcerative colitis, and some scholars have described it as a "barrier organ disease." While the Notch signalling pathway affects a series of cellular processes, including proliferation, differentiation, development, migration, and apoptosis. Therefore, it can regulate intestinal stem cells, CD4+ T cells, innate lymphoid cells, macrophages, and intestinal microbiota and intervene in the chemical, physical, immune, and biological mucosal barriers in cases of ulcerative colitis. The Notch signalling pathway associated with the pathogenesis of ulcerative colitis has distinct characteristics, with good regulatory effects on the mucosal barrier. However, research on ulcerative colitis has mainly focused on immune regulation, anti-inflammatory activity, and antioxidant stress; therefore, the study of the Notch signalling pathway suggests the possibility of understanding the pathogenesis of ulcerative colitis from another perspective. In this article we explore the role and mechanism of the Notch signalling pathway in the pathogenesis of ulcerative colitis from the perspective of the intestinal mucosal barrier to provide new targets and theoretical support for further research on the pathogenesis and clinical treatment of ulcerative colitis.

Prolonged NHE Activation may be both Cause and Outcome of Cytokine Release Syndrome in COVID-19

The release of cytokines and chemokines such as IL-1β, IL-2, IL-6, IL-7, IL-10, TNF-α, IFN-γ, CCL2, CCL3, and CXCL10 is increased in critically ill patients with COVID-19. Excessive cytokine release during COVID-19 is related to increased morbidity and mortality. Several mechanisms are put forward for cytokine release syndrome during COVID-19. Here we have mentioned novel pathways. SARS-CoV-2 increases angiotensin II levels by rendering ACE2 nonfunctional. Angiotensin II causes cytokine release via AT₁ and AT₂ receptors. Moreover, angiotensin II potently stimulates the Na+/H+ exchanger (NHE). It is a pump found in the membranes of many cells that pumps Na+ inward and H+ outward. NHE has nine isoforms. NHE1 is the most common isoform found in endothelial cells and many cells. NHE is involved in keeping the intracellular pH within physiological limits. When the intracellular pH is acidic, NHE is activated, bringing the intracellular pH to physiological levels, ending its activity. Sustained NHE activity is highly pathological and causes many problems. Prolonged NHE activation in COVID-19 may cause a decrease in intracellular pH through H+ ion accumulation in the extracellular area and subsequent redox reactions. The activation reduces the intracellular K+ concentration and leads to Na+ and Ca²⁺ overload. Increased ROS can cause intense cytokine release by stimulating NF-κB and NLRP3 inflammasomes. Cytokines also cause overstimulation of NHE. As the intracellular pH decreases, SARS-CoV-2 rapidly infects new cells, increasing the viral load. This vicious circle increases morbidity and mortality in patients with COVID-19. On the other hand, SARS-CoV-2 interaction with NHE3 in intestinal tissue is different from other tissues. SARS-CoV-2 can trigger CRS via NHE3 inhibition by disrupting the intestinal microbiota. This review aimed to help develop new treatment models against SARS-CoV-2- induced CRS by revealing the possible effects of SARS-CoV-2 on the NHE.

The SLC9A-C Mammalian Na+/H+ Exchanger Family: Molecules, Mechanisms, and Physiology

Na⁺/H⁺ exchangers play pivotal roles in the control of cell and tissue pH by mediating the electroneutral exchange of Na⁺ and H⁺ across cellular membranes. They belong to an ancient family of highly evolutionarily conserved proteins, and they play essential physiological roles in all phyla. In this review, we focus on the mammalian Na⁺/H⁺ exchangers (NHEs), the solute carrier (SLC) 9 family. This family of electroneutral transporters constitutes three branches: SLC9A, -B, and -C. Within these, each isoform exhibits distinct tissue expression profiles, regulation, and physiological roles. Some of these transporters are highly studied, with hundreds of original articles, and some are still only rudimentarily understood. In this review, we present and discuss the pioneering original work as well as the current state-of-the-art research on mammalian NHEs. We aim to provide the reader with a comprehensive view of core knowledge and recent insights into each family member, from gene organization over protein structure and regulation to physiological and pathophysiological roles. Particular attention is given to the integrated physiology of NHEs in the main organ systems. We provide several novel analyses and useful overviews, and we pinpoint main remaining enigmas, which we hope will inspire novel research on these highly versatile proteins.

Impairing of gill health through decreasing immune function and structural integrity of grass carp (Ctenopharyngodon idella) fed graded levels dietary lipids after challenged with Flavobacterium columnare

The current study conducted to investigate the hypothesis that low or excess levels of lipids increased the gill rot morbidity through impairing the immune function and structural integrity in the gill of grass carp (Ctenopharyngodon idella). A total of 540 young grass carp with an average initial weight of 261.41 ± 0.53 g were fed diets containing six graded levels of lipids at 0.59%, 2.14%, 3.60%, 5.02%, 6.66% and 8.01% diets for 8 weeks. After the growth trial, fish were challenged with Flavobacterium columnare for 3 days. The results indicated that compared with optimal lipids supplementation (2.14%-8.01% lipids diets), low or excess levels of lipids impaired fish immune function through declining the activities of humoral compounds, down-regulated the mRNA levels of anti-inflammatory cytokines, inhibitor of κBα (IκBα) and ribosomal p70S6 kinase (S6K1), and up-regulated pro-inflammatory cytokines, nuclear factor κB p65 (NF-κB p65) (not p52), IκB kinase α (IKKα) (not IKKβ), IKKγ and eIF4E-binding protein (4EBP) in the gill of young grass carp. In addition, low or excess levels of lipids decreased young grass carp physical barrier function through down-regulating the mRNA levels of ZO-1 (rather than ZO-2b), Claudin b, c, 3, 12, 15a, 15b, 7b, 7a and Occludin through MAPKK 6/p38 MAPK/MLCK signaling molecules, decreasing antioxidant ability via Kelch-like ECH-associating protein 1a (Keap1a)/NF-E2-related factor 2 (Nrf2) signaling molecules, and down-regulating the mRNA levels of B-cell lymphoma-2 (Bcl-2) and inhibitor of apoptosis protein (IAP) and up-regulating the mRNA levels of apoptotic protease activating factor-1 (Apaf-1), Caspase-3, -8 and -9 and Fas ligand (FasL) in the gill of grass carp. Based on the quadratic regression analysis for the gill rot morbidity, C3 and MDA contents, the dietary lipids requirements for young grass carp have been estimated to be 5.60%, 6.01% and 4.58% diets.

Amelioration of Lipopolysaccharide-Induced Acute Lung Injury in Rats by Na-H Exchanger-1 Inhibitor Amiloride Is Associated with Reversal of ERK Mitogen-Activated Protein Kinase

Background

Na-H exchanger-1 (NHE-1) is expressed in the lung of rats. Accumulating evidence shows that Na-H exchangers are involved in inflammation. Amiloride, an inhibitor of NHE-1, inhibits the activation of macrophages and endothelial cells and reduces their production of cytokines. Since these processes have been implicated in acute lung injury (ALI) induced by lipopolysaccharide (LPS), we examined the protective effect of amiloride on ALI induced by LPS in rats.

Material and Methods

ALI in specific pathogen-free male Sprague-Dawley rats was induced by an intravenous injection of 6 mg/kg LPS. Amiloride pretreated rats received an intravenous injection of 10 mg/kg amiloride 30 min before the administration of LPS. Controls received normal saline in a similar manner. All animals were sacrificed 6 h after LPS or normal saline administration. The degree of ALI was assessed by wet-to-dry weight ratio (W/D) and lung histological examination. Neutrophilic infiltration was determined by myeloperoxidase (MPO) activity in lung tissue. Concentrations of total protein (TP), tumor necrosis factor-alpha (TNF-α), and macrophage inflammatory protein-2 (MIP-2) in bronchoalveolar lavage fluid (BALF) were also measured. Expression of NHE-1 and mitogen-activated protein kinase (MAPK) p38, p-p38, ERK, and p-ERK was evaluated by western blot analysis.

Results

Pretreatment with amiloride significantly reduced the increase in W/D, ALI score, lung tissue MPO activity, concentrations of TP, TNF-α, and MIP-2 in BALF, resulting in attenuation of ALI induced by LPS. Meanwhile, levels of NHE-1 and p-ERK proteins were reversed, whereas that of p-p38 was not.

Conclusions

These findings suggest that NHE-1 inhibitor amiloride could attenuate ALI induced by LPS in rats. This effect is mediated through reversal of ERK.

SLC9 Gene Family: Function, Expression, and Regulation

The Slc9 family of Na⁺ /H⁺ exchangers (NHEs) plays a critical role in electroneutral exchange of Na⁺ and H⁺ in the mammalian intestine as well as other absorptive and secretory epithelia of digestive organs. These transport proteins contribute to the transepithelial Na⁺ and water absorption, intracellular pH and cellular volume regulation as well as the electrolyte, acid-base, and fluid volume homeostasis at the systemic level. They also influence the function of other membrane transport mechanisms, affect cellular proliferation and apoptosis as well as cell migration, adherence to the extracellular matrix, and tissue repair. Additionally, they modulate the extracellular milieu to facilitate other nutrient absorption and to regulate the intestinal microbial microenvironment. Na⁺ /H⁺ exchange is inhibited in selected gastrointestinal diseases, either by intrinsic factors (e.g., bile acids, inflammatory mediators) or infectious agents and associated bacterial toxins. Disrupted NHE activity may contribute not only to local and systemic electrolyte imbalance but also to the disease severity via multiple mechanisms. In this review, we describe the cation proton antiporter superfamily of Na⁺ /H⁺ exchangers with a particular emphasis on the eight SLC9A isoforms found in the digestive tract, followed by a more integrative description in their roles in each of the digestive organs. We discuss regulatory mechanisms that determine the function of Na⁺ /H⁺ exchangers as pertinent to the digestive tract, their regulation in pathological states of the digestive organs, and reciprocally, the contribution of dysregulated Na⁺ /H⁺ exchange to the disease pathogenesis and progression. © 2018 American Physiological Society. Compr Physiol 8:555-583, 2018.

Mendelian Disease Associations Reveal Novel Insights into Inflammatory Bowel Disease

Background

Monogenic diseases have been shown to contribute to complex disease risk and may hold new insights into the underlying biological mechanism of Inflammatory Bowel Disease (IBD).

Methods

We analyzed Mendelian disease associations with IBD using over 55 million patients from the Optum's deidentified electronic health records dataset database. Using the significant Mendelian diseases, we performed pathway enrichment analysis and constructed a model using gene expression datasets to differentiate Crohn's disease (CD), ulcerative colitis (UC), and healthy patient samples.

Results

We found 50 Mendelian diseases were significantly associated with IBD, with 40 being significantly associated with both CD and UC. Our results for CD replicated those from previous studies. Pathways that were enriched consisted of mainly immune and metabolic processes with a focus on tolerance and oxidative stress. Our 3-way classifier for UC, CD, and healthy samples yielded an accuracy of 72%.

Conclusions

Mendelian diseases that are significantly associated with IBD may reveal novel insights into the genetic architecture of IBD.

Environmental carcinogenesis and pH homeostasis: Not only a matter of dysregulated metabolism

According to the World Health Organization, around 20% of all cancers would be due to environmental factors. Among these factors, several chemicals are indeed well recognized carcinogens. The widespread contaminant benzo[a]pyrene (B[a]P), an often used model carcinogen of the polycyclic aromatic hydrocarbons' family, has been suggested to target most, if not all, cancer hallmarks described by Hanahan and Weinberg. It is classified as a group I carcinogen by the International Agency for Research on Cancer; however, the precise intracellular mechanisms underlying its carcinogenic properties remain yet to be thoroughly defined. Recently, the pH homeostasis, a well known regulator of carcinogenic processes, was suggested to be a key actor in both cell death and Warburg-like metabolic reprogramming induced upon B[a]P exposure. The present review will highlight those data with the aim of favoring research on the role of H⁺ dynamics in environmental carcinogenesis.

Pathophysiology of Intestinal Na+/H+ exchange

Several members of the SLC9A family of Na⁺/H⁺ exchangers are expressed in the gut, with varying expression patterns and cellular localization. Not only do they participate in the regulation of basic epithelial cell functions, including control of transepithelial Na⁺ absorption, intracellular pH (pH _i ), cell volume, and nutrient absorption, but also in cellular proliferation, migration, and apoptosis. Additionally, they modulate the extracellular milieu in order to facilitate other nutrient absorption and to regulate the intestinal microbial microenvironment. Na⁺/H⁺ exchangers are frequent targets of inhibition in gastrointestinal pathologies, either by intrinsic factors (e.g. bile acids, inflammatory mediators) or infectious agents and associated microbial toxins. Based on emerging evidence, disruption of NHE activity via impaired expression or function of respective isoforms may contribute not only to local and systemic electrolyte imbalance, but also to the disease severity via multiple mechanisms. Here, we review the current state of knowledge about the roles Na⁺/H⁺ exchangers play in the pathogenesis of disorders of diverse origin and affecting a range of GI tissues.

The glucocorticoid budesonide has protective and deleterious effects in experimental colitis in mice

Glucocorticoids are widely used for the management of inflammatory bowel disease, albeit with known limitations for long-term use and relevant adverse effects. In turn, they have harmful effects in experimental colitis. We aimed to explore the mechanism and possible implications of this phenomenon. Regular and microbiota depleted C57BL/6 mice were exposed to dextran sulfate sodium (DSS) to induce colitis and treated with budesonide. Colonic inflammation and animal status were compared. In vitro epithelial models of wound healing were used to confirm the effects of glucocorticoids. Budesonide was also tested in lymphocyte transfer colitis. Budesonide (1-60μg/day) exerted substantial colonic antiinflammatory effects in DSS colitis. At the same time, it aggravated body weight loss, increased rectal bleeding, and induced general deterioration of animal status, bacterial translocation and endotoxemia. As a result, there was an associated increase in parameters of sepsis, such as plasma NOx, IL-1β, IL-6, lung myeloperoxidase and iNOS, as well as significant hypothermia. Budesonide also enhanced DSS induced colonic damage in microbiota depleted mice. These effects were correlated with antiproliferative effects at the epithelial level, which are expected to impair wound healing. In contrast, budesonide had significant but greatly diminished deleterious effects in noncolitic mice or in mice with lymphocyte transfer colitis. We conclude that budesonide weakens mucosal barrier function by interfering with epithelial dynamics and dampening the immune response in the context of significant mucosal injury, causing sepsis. This may be a contributing factor, at least in part, limiting clinical usefulness of corticoids in inflammatory bowel disease.

Role of epithelial ion transports in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder with a complex pathogenesis. Diarrhea is a highly prevalent and often debilitating symptom of IBD patients that results, at least in part, from an intestinal hydroelectrolytic imbalance. Evidence suggests that reduced electrolyte absorption is more relevant than increased secretion to this disequilibrium. This systematic review analyses and integrates the current evidence on the roles of epithelial Na(+)-K(+)-ATPase (NKA), Na(+)/H(+) exchangers (NHEs), epithelial Na(+) channels (ENaC), and K(+) channels (KC) in IBD-associated diarrhea. NKA is the key driving force of the transepithelial ionic transport and its activity is decreased in IBD. In addition, the downregulation of apical NHE and ENaC and the upregulation of apical large-conductance KC all contribute to the IBD-associated diarrhea by lowering sodium absorption and/or increasing potassium secretion.

Lineage-specific expression of bestrophin-2 and bestrophin-4 in human intestinal epithelial cells

Intestinal epithelial cells (IECs) regulate the absorption and secretion of anions, such as HCO3^- or Cl^-. Bestrophin genes represent a newly identified group of calcium-activated Cl^- channels (CaCCs). Studies have suggested that, among the four human bestrophin-family genes, bestrophin-2 (BEST2) and bestrophin-4 (BEST4) might be expressed within the intestinal tissue. Consistently, a study showed that BEST2 is expressed by human colonic goblet cells. However, their precise expression pattern along the gastrointestinal tract, or the lineage specificity of the cells expressing these genes, remains largely unknown. Here, we show that BEST2 and BEST4 are expressed in vivo, each in a distinct, lineage-specific manner, in human IECs. While BEST2 was expressed exclusively in colonic goblet cells, BEST4 was expressed in the absorptive cells of both the small intestine and the colon. In addition, we found that BEST2 expression is significantly down-regulated in the active lesions of ulcerative colitis, where goblet cells were depleted, suggesting that BEST2 expression is restricted to goblet cells under both normal and pathologic conditions. Consistently, the induction of goblet cell differentiation by a Notch inhibitor, LY411575, significantly up-regulated the expression of not BEST4 but BEST2 in MUC2-positive HT-29 cells. Conversely, the induction of absorptive cell differentiation up-regulated the expression of BEST4 in villin-positive Caco-2 cells. In addition, we found that the up- or down-regulation of Notch activity leads to the preferential expression of either BEST4 or BEST2, respectively, in LS174T cells. These results collectively confirmed that BEST2 and BEST4 could be added to the lineage-specific genes of humans IECs due to their abilities to clearly identify goblet cells of colonic origin and a distinct subset of absorptive cells, respectively.

High sodium augments angiotensin II-induced vascular smooth muscle cell proliferation through the ERK 1/2-dependent pathway

Angiotensin II (Ang II)-induced vascular injury is exacerbated by high-salt diets. This study examined the effects of high-sodium level on Ang II-induced cell proliferation in rat vascular smooth muscle cells (VSMCs). The cells were cultured in a standard medium containing 137.5 mmol l(-1) of sodium. The high-sodium medium (140 mmol l(-1)) contained additional sodium chloride. Extracellular signal-regulated kinase (ERK) 1/2 phosphorylation was determined by western blot analysis. Cell proliferation was evaluated by [(3)H]-thymidine incorporation. Ang II (100 nmol l(-1)) significantly increased ERK 1/2 phosphorylation and cell proliferation in the both medium containing standard sodium and high sodium. High-sodium level augmented Ang II-induced ERK 1/2 phosphorylation and cell proliferation compared with standard sodium. Pre-treatment with candesartan (1 μmol l(-1), Ang II type 1 receptor blocker) or PD98095 (10 μmol l(-1), ERK kinase iinhibitor) abolished the proliferative effect induced by high sodium/Ang II. Pre-treatment with 5-N,N-hexamethylene amiloride (30 μmol l(-1), Na(+)/H(+) exchanger type 1 (NHE-1) inhibitor), but not SN-6 (10 μmol l(-1), Na(+)/Ca(2+) exchanger inhibitor) or ouabain (1 mmol l(-1), Na(+)/K(+)-ATPase inhibitor) attenuated ERK 1/2 phosphorylation or cell proliferation. Osmotic pressure or chloride had no effect on Ang II-induced proliferative changes. High-sodium level did not affect Ang II receptor expression. Ang II increased intracellular pH via NHE-1 activation, and high-sodium level augmented the pH increase induced by Ang II. These data suggest that high-sodium level directly augments Ang II-induced VSMC proliferation through NHE-1- and ERK 1/2-dependent pathways and may offer new insights into the mechanisms of vascular remodeling by high-sodium/Ang II.

Role of NHE1 in Nociception

Intracellular pH is a fundamental parameter to cell function that requires tight homeostasis. In the absence of any regulation, excessive acidification of the cytosol would have the tendency to produce cellular damage. Mammalian Na(+)/H(+) exchangers (NHEs) are electroneutral Na(+)-dependent proteins that exchange extracellular Na(+) for intracellular H(+). To date, there are 9 identified NHE isoforms where NHE1 is the most ubiquitous member, known as the housekeeping exchanger. NHE1 seems to have a protective role in the ischemia-reperfusion injury and other inflammatory diseases. In nociception, NHE1 is found in neurons along nociceptive pathways, and its pharmacological inhibition increases nociceptive behavior in acute pain models at peripheral and central levels. Electrophysiological studies also show that NHE modulates electrical activity of primary nociceptive terminals. However, its role in neuropathic pain still remains controversial. In humans, NHE1 may be responsible for inflammatory bowel diseases since its expression is reduced in Crohn's disease and ulcerative colitis. The purpose of this work is to provide a review of the evidence about participation of NHE1 in the nociceptive processing.

The bradykinin B(2) receptor induces multiple cellular responses leading to the proliferation of human renal carcinoma cell lines

Background

The vasoactive peptide bradykinin (BK) acts as a potent growth factor for normal kidney cells, but there have been few studies on the role of BK in renal cell carcinomas.

Purpose

In this study, we tested the hypothesis that BK also acts as a mitogen in kidney carcinomas, and explored the effects of BK in human renal carcinoma A498 cells.

Methods

The presence of mRNAs for BK B₁ and BK B₂ receptors in A498 cells was demonstrated by reverse transcription–polymerase chain reaction. To study BK signaling pathways, we employed fluorescent measurements of intracellular Ca²⁺, measured changes in extracellular pH as a reflection of Na⁺/H⁺ exchange (NHE) with a Cytosensor microphysiometer, and assessed extracellular signal-regulated kinase (ERK) activation by Western blotting.

Results

Exposure to 100 nM of BK resulted in the rapid elevation of intracellular Ca²⁺, caused a ≥30% increase in NHE activity, and a ≥300% increase in ERK phosphorylation. All BK signals were blocked by HOE140, a BK B₂ receptor antagonist, but not by a B₁ receptor antagonist. Inhibitor studies suggest that BK-induced ERK activation requires phospholipase C and protein kinase C activities, and is Ca²⁺/calmodulin-dependent. The amiloride analog 5-(N-methyl-N-isobutyl)-amiloride (MIA) blocked short-term NHE activation and inhibited ERK phosphorylation, suggesting that NHE is critical for ERK activation by BK. BK induced an approximately 40% increase in the proliferation of A498 cells as assessed by bromodeoxyuridine uptake. This effect was blocked by the ERK inhibitor PD98059, and was dependent on NHE activity.

Conclusion

We conclude that BK exerts mitogenic effects in A498 cells via the BK B₂ receptor activation of growth-associated NHE and ERK.

Fibronectin stimulates migration through lipid raft dependent NHE-1 activation in mouse embryonic stem cells: involvement of RhoA, Ca(2+)/CaM, and ERK

BACKGROUND

Extracellular matrix (ECM) components and intracellular pH (pH(i)) may serve as regulators of cell migration in various cell types.

METHODS

The Oris migration assay was used to assess the effect of fibronectin (FN) on cell motility. The Na(+)/H(+) exchanger (NHE)-1 activity was evaluated by measuring pH(i) and [(22)Na(+)] uptake. To examine activated signaling molecules, western blot analysis and immunoprecipitation was performed.

RESULTS

ECM components (FN, laminin, fibrinogen, and collagen type I) increased [(22)Na(+)] uptake, pH(i), and cell migration. In addition, FN-induced increase of cell migration was inhibited by NHE-1 inhibitor amiloride or NHE-1-specific siRNA. FN selectively increased the mRNA and protein expression of NHE-1, but not that of NHE-2 or NHE-3. FN binds integrin β1 and subsequently stimulates caveolin-1 phosphorylation and Ca(2+) influx. Then, NHE-1 is phosphorylated by RhoA and Rho kinases, and Ca(2+)/calmodulin (CaM) signaling elicits complex formation with NHE-1, which is enriched in lipid raft/caveolae microdomains of the plasma membrane. Activation of NHE-1 continuously induces an increase of [(22)Na(+)] uptake and pH(i). Finally, NHE-1-dependent extracellular signal-regulated kinase (ERK) 1/2 phosphorylation enhanced matrix metalloproteinase-2 (MMP-2) and filamentous-actin (F-actin) expression, partially contributing to the regulation of embryonic stem cells (ESCs) migration.

CONCLUSIONS

FN stimulated mESCs migration and proliferation through NHE-1 activation, which were mediated by lipid raft-associated caveolin-1, RhoA/ROCK, and Ca(2+)/CaM signaling pathways.

GENERAL SIGNIFICANCE

The precise role of NHE in the modulation of ECM-related physiological functions such as proliferation and migration remains poorly understood. Thus, this study analyzed the relationship between FN and NHE in regulating the migration of mouse ESCs and their related signaling pathways.

Modeling natural anti-inflammatory compounds by molecular topology

One of the main pharmacological problems today in the treatment of chronic inflammation diseases consists of the fact that anti-inflammatory drugs usually exhibit side effects. The natural products offer a great hope in the identification of bioactive lead compounds and their development into drugs for treating inflammatory diseases. Computer-aided drug design has proved to be a very useful tool for discovering new drugs and, specifically, Molecular Topology has become a good technique for such a goal. A topological-mathematical model, obtained by linear discriminant analysis, has been developed for the search of new anti-inflammatory natural compounds. An external validation obtained with the remaining compounds (those not used in building up the model), has been carried out. Finally, a virtual screening on natural products was performed and 74 compounds showed actual anti-inflammatory activity. From them, 54 had been previously described as anti-inflammatory in the literature. This can be seen as a plus in the model validation and as a reinforcement of the role of Molecular Topology as an efficient tool for the discovery of new anti-inflammatory natural compounds.

Cross-reactivity of acid-sensing ion channel and Na⁺-H⁺ exchanger antagonists with nicotinic acetylcholine receptors

Nicotinic acetylcholine receptors (nAChRs) are widely distributed throughout the mammalian central and peripheral nervous systems, where they contribute to neuronal excitability and synaptic communication. It has been reported that nAChRs are modulated by BK channels and that BK channels, in turn, are inhibited by acid-sensing ion channels (ASICs). Here we investigate the possible functional interaction between these channels in medial habenula (MHb) neurones. We report that selective antagonists of large-conductance calcium-activated potassium channels and ASIC1a channels, paxilline and psalmotoxin 1, respectively, did not induce detectable changes in nicotine-evoked currents. In contrast, the non-selective ASIC and Na(+)-H(+) exchanger (NHE1) antagonists, amiloride and its analogues, suppressed nicotine-evoked responses in MHb neurones of wild-type and ASIC2 null mice, excluding a possible involvement of ASIC2 in the nAChR inhibition by amiloride. Zoniporide, a more selective inhibitor of NHE1, reversibly inhibited α3β4-, α7- and α4-containing (*) nAChRs in Xenopus oocytes and in brain slices, as well as in PS120 cells deficient in NHE1 and virally transduced with nAChRs, suggesting a generalized effect of zoniporide in most neuronal nAChR subtypes. Independently from nAChR antagonism, zoniporide profoundly blocked synaptic transmission onto MHb neurones without affecting glutamatergic and GABA receptors. Taken together, these results indicate that amiloride and zoniporide, which are clinically used to treat hypertension and cardiovascular disease, have an inhibitory effect on neuronal nAChRs when used experimentally at high doses. The possible cross-reactivity of these compounds with nAChRs in vivo will require further investigation.

Basolateral LPS inhibits NHE3 and HCOFormula absorption through TLR4/MyD88-dependent ERK activation in medullary thick ascending limb

Sepsis is associated with defects in renal tubule function, but the underlying mechanisms are incompletely understood. Recently, we demonstrated that Gram-negative bacterial lipopolysaccharide (LPS) inhibits HCO(3)(-) absorption in the medullary thick ascending limb (MTAL) through activation of Toll-like receptor 4 (TLR4). Here, we examined the mechanisms responsible for inhibition of HCO(3)(-) absorption by basolateral LPS. Adding LPS to the bath decreased HCO(3)(-) absorption by 30% in rat and mouse MTALs perfused in vitro. The inhibition of HCO(3)(-) absorption was eliminated by the mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK)/ERK inhibitors U0126 and PD98059. LPS induced a rapid (<15 min) and sustained (up to 60 min) increase in ERK phosphorylation in microdissected MTALs that was blocked by PD98059. The effects of basolateral LPS to activate ERK and inhibit HCO(3)(-) absorption were eliminated in MTALs from TLR4(-/-) and myeloid differentiation factor 88 (MyD88)(-/-) mice but were preserved in MTALs from TIR (Toll/interleukin-1 receptor) domain-containing adapter-inducing interferon-β (Trif)(-/-) mice. Basolateral LPS decreased apical Na(+)/H(+) exchanger 3 NHE3 activity through a decrease in maximal velocity (V(max)). The inhibition of NHE3 by LPS was eliminated by MEK/ERK inhibitors. LPS inhibited HCO(3)(-) absorption despite the presence of physiological stimuli that activate ERK in the MTAL. We conclude that basolateral LPS inhibits HCO(3)(-) absorption in the MTAL through activation of a TLR4/MyD88/MEK/ERK pathway coupled to inhibition of NHE3. These studies identify NHE3 as a target of TLR4 signaling in the MTAL and show that bacterial molecules can impair the absorptive functions of renal tubules through inhibition of this exchanger. The ERK pathway links TLR4 to downstream modulation of ion transport proteins and represents a potential target for treatment of sepsis-induced renal tubule dysfunction.

New therapeutic targets in ulcerative colitis: the importance of ion transporters in the human colon

BACKGROUND

The absorption of water and ions (especially Na(+) and Cl(-)) is an important function of colonic epithelial cells in both physiological and pathophysiological conditions. Despite the comprehensive animal studies, there are only scarce available data on the ion transporter activities of the normal and inflamed human colon.

METHODS

In this study, 128 healthy controls and 69 patients suffering from ulcerative colitis (UC) were involved. We investigated the expressional and functional characteristics of the Na(+)/H(+) exchangers (NHE) 1-3, the epithelial sodium channel (ENaC), and the SLC26A3 Cl(-)/HCO 3- exchanger downregulated in adenoma (DRA) in primary colonic crypts isolated from human biopsy and surgical samples using microfluorometry, patch clamp, and real-time reverse-transcription polymerase chain reaction (RT-PCR) techniques.

RESULTS

Data collected from colonic crypts showed that the activities of electroneutral (via NHE3) and the electrogenic Na(+) absorption (via ENaC) are in inverse ratio to each other in the proximal and distal colon. We found no significant differences in the activity of NHE2 in different segments of the colon. Surface cell Cl(-)/HCO 3- exchange is more active in the distal part of the colon. Importantly, both sodium and chloride absorptions are damaged in UC, whereas NHE1, which has been shown to promote immune response, is upregulated by 6-fold.

CONCLUSIONS

These results open up new therapeutic targets in UC.

Resuscitation-induced intestinal edema and related dysfunction: state of the science

High volume resuscitation and damage control surgical methods, while responsible for significantly decreasing morbidity and mortality from traumatic injuries, are associated with pathophysiologic derangements that lead to subsequent end organ edema and dysfunction. Alterations in hydrostatic and oncotic pressures frequently result in intestinal edema and subsequent dysfunction. The purpose of this review is to examine the principles involved in the development of intestinal edema, current and historical models for the study of edema, effects of edema on intestinal function (particularly ileus), molecular mediators governing edema-induced dysfunction, potential role of mechanotransduction , and therapeutic effects of hypertonic saline. We review the current state of the science as it relates to resuscitation induced intestinal edema and resultant dysfunction.

Suppression of Na+/H+ exchanger isoform-3 in human inflammatory bowel disease: lack of reversal by 5'-aminosalicylate treatment

OBJECTIVE

Na+/H+ exchanger isoform 3 (NHE-3) is responsible for net uptake of NaCl and water from the gastrointestinal (GI) tract. However, its status in human inflammatory bowel diseases (IBDs) such as ulcerative colitis(UC) and Crohn's disease (CD) remains poorly understood. The aim of this study was to investigate the underlying mechanism of NHE-3 isoform expression and its modulation by 5'-aminosalicylate in human CD and UC.

MATERIAL AND METHODS

Subjects were divided into three groups: 1) controls; 2) untreated/new IBD cases (n = 13) and 3) 5'-aminosalicylate-treated IBD patients (n = 13). Subjects presenting with abdominal pain but with endoscopically normal colons served as normal controls. Inflammation was confirmed by the level of myeloperoxidase (MPO) activity, malondialdehyde (MDA) concentrations and by histologic evaluation. Expressions of NHE-3 protein and mRNA, sodium pump activity and IL-1beta and TNF-alpha mRNA were estimated in the colonic biopsies using ECL-Western blot analysis,reverse transcription-polymerase chain reaction (RT-PCR) and enzyme assays.

RESULTS

The level of NHE-3 protein and sodium pump activity was reduced (p < 0.05) in both the untreated and treated CD and UC patients. NHE-3 mRNA was reduced only in CD patients but not in those with UC. The treatment reversed the symptoms, but levels of MPO activity, MDA concentration, IL-1beta, TNF-alpha and infiltration of inflammatory cells remained high with the exception of IL-1beta mRNA in the treated patients.

CONCLUSIONS

NHE-3 suppression is regulated differentially in CD and UC, which together with suppression of sodium pump activity will reduce NaCl and water uptake from the colonic lumen. These findings suggest a role of TNF-a in the regulation of NHE-3 expression in IBD.

Cellular edema regulates tissue capillary perfusion after hemorrhage resuscitation

BACKGROUND

Hemorrhage-induced activation of endothelial cell Na+/H+ -exchanger results in cellular swelling, which physically impedes capillary filling and compromises gut perfusion. We hypothesized that correction of the vascular volume deficit by conventional resuscitation does not improve capillary filling unless cellular swelling is prevented. Also, we hypothesized that adjunctive direct peritoneal resuscitation (DPR) with topical peritoneal dialysis solution (Delflex; Fresenius USA, Inc., Ogden, Ut) enhances capillary filling and gut perfusion by mechanisms that are independent of the Na+/H+ function.

METHODS

In vivo intravital videomicroscopy and Doppler velocimeter were used by us to measure microvascular diameter and flow, capillary filling (index of functional capillary density, FCD), and endothelial cell function in the terminal ileum of anesthetized rats. Rats were bled to 50% mean arterial pressure for 60 min and resuscitated with the shed blood plus 2 volumes of saline (conventional resuscitation). Prevention of endothelial cell swelling was achieved with topical amiloride (specific Na+/H+ inhibitor) in the tissue bath before hemorrhage or simultaneously with conventional resuscitation. DPR was simulated by instillation of Delflex in the tissue bath as adjunctive to conventional resuscitation. Sham no hemorrhage group and a simulated DPR group that received topical amiloride treatment served as controls.

RESULTS

Conventional resuscitation from hemorrhagic shock restored and maintained central hemodynamics but caused progressive and persistent intestinal vasoconstriction and hypoperfusion associated with low FCD and endothelial cell dysfunction. Prevention of endothelial cell swelling when combined with conventional resuscitation, preserved endothelial cell function, and restored local intestinal microvascular variables to near-prehemorrhage levels. Simulated adjunctive DPR produced rapid, sustained, and generalized vasodilation associated with restoration of endothelial cell function, and maximum recruitment of FCD independent of the Na+/H+ -exchanger function.

CONCLUSIONS

Paradoxical endothelial cell swelling occurs early during hemorrhagic shock because of activation of the Na+/H+ exchanger. This cellular edema, which is not resolved by correction of the vascular volume deficit, explains the persistent postresuscitation endothelial cell dysfunction and gut hypoperfusion. Simulated adjunctive DPR in this study reversed endothelial cell swelling and enhanced gut perfusion by mechanisms that are independent of the Na+/H+ exchanger activity.

The adenosine A2A receptor agonist CGS 21680 fails to ameliorate the course of dextran sulphate-induced colitis in mice

OBJECTIVE

In this study we investigated the effect of CGS 21680 (2-p-(2-Carboxyethyl)phenethylamino-5-N-ethylcarboxamidoadenosine hydrochloride), an adenosine A2A receptor agonist, in a model of dextran sulphate sodium (DSS)-induced colitis.

METHODS

NMRI mice were fed 5 % (w/v) DSS, and were treated intraperitoneally with 0.5 mg/kg CGS 21680 or vehicle for 10 days. Changes of bodyweight, colon length, the incidence of rectal bleeding, levels of macrophage inflammatory protein (MIP)-1alpha, MIP-2, interferon gamma, interleukin (IL)-1beta, IL-12 and tumour necrosis factor-alpha from homogenates of colon biopsies, and the release of [3H]acetylcholine (ACh) from longitudinal muscle strip were determined.

RESULTS

DSS significantly decreased bodyweight, colon length, and it increased the incidence of rectal bleeding and levels of MIP-1alpha, MIP-2 and IL-1beta compared to DSS-untreated animals. CGS 21680 had no effect on these changes. No change could be observed in release of ACh in DSS-induced colitis with or without CGS 21680.

CONCLUSION

In summary, CGS 21680 is ineffective in ameliorating DSS-induced colitis in mice.

Short-term effect on intestinal epithelial Na+/H+ exchanger by Giα1,2-coupled 5-HT1A and Gq/11-coupled 5-HT2 receptors

The present study evaluated the effect of 5-hydroxytryptamine (5-HT) on intestinal Na(+)/H(+) exchanger (NHE) activity and the cellular signaling pathways involved in T84 cells. T84 cells express endogenous NHE1 and NHE2 proteins, detected by immunoblotting, but not NHE3. The rank order for inhibition of NHE activity in acid-loaded T84 cells was 5-(N-ethyl-N-isopropyl)-amiloride (EIPA; IC(50)=519 [465, 579] nM)>cariporide (IC(50)=630 [484, 819] nM)>amiloride (IC(50)=19 [16, 24] microM); the NHE3 inhibitor S3226 was found to be devoid of effect. This different inhibitory sensitivity indicates that both NHE1 and NHE2 isoforms may play an active role in Na(+)-dependent intracellular pH (pH(i)) recovery in T84 cells. Short-term exposure (0.5 h) of T84 cells to 5-HT increased NHE activity in a concentration-dependent manner. The stimulation induced by 5-HT (30 microM) was partially inhibited by both WAY 100135 (300 nM) and ketanserin (300 nM), antagonists of 5-HT(1A) and 5-HT(2) receptors, respectively. NHE activity was significantly increased by 8-OH-DPAT and alpha-methyl-5-HT, agonists of, respectively, 5-HT(1A) and 5-HT(2) receptors. An incubation of T84 cells with anti-G(s) and anti-G(beta) antibodies complexed with lipofectin did not prevent the 5-HT-induced stimulation of NHE activity. Overnight treatment with anti-G(ialpha1,2) and anti-G(q/11) antibodies complexed with lipofectin blocked the stimulatory effect induced by 8-OH-DPAT and alpha-methyl-5-HT, respectively. It is concluded that in T84 cells 5-HT enhances intestinal NHE activity through stimulation of G(ialpha1,2)-coupled 5-HT(1A) and G(q/11)-coupled 5-HT(2) receptors.

Regulation of mitogen-activated protein kinase pathways by the plasma membrane Na+/H+ exchanger, NHE1

The mitogen-activated protein kinases (MAPKs), including extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK, play a major role in the regulation of pivotal cellular processes such as cell death/survival balance, cell cycle progression, and cell migration. MAPK activity is regulated by a three-tiered phosphorelay system, which is in turn regulated by a complex network of signaling events and scaffolding proteins. The ubiquitous plasma membrane Na(+)/H(+) exchanger NHE1 is activated by, and implicated in, the physiological/pathophysiological responses to many of the same stimuli that modulate MAPK activity. While under some conditions, NHE1 is regulated by MAPKs, a number of studies have, conversely, implicated NHE1 in the regulation of MAPK activity. Here, we discuss the current evidence indicating the involvement of NHE1 in MAPK regulation, the mechanisms by which this may occur, and the possible physiological and pathophysiological relevance of this phenomenon.

Amiloride moderates increased gut permeability and diminishes mesenteric lymph-mediated priming of neutrophils in trauma/hemorrhagic shock

BACKGROUND

Amiloride, an inhibitor of Na+/H+ exchangers and Na+ channels has been shown recently to ameliorate both gut and lung injury in rats subjected to a combined insult of trauma and hemorrhagic shock (T/HS). We have shown previously that mesenteric lymph duct ligation prevents T/HS-induced lung endothelial injury and neutrophil activation, suggesting that toxic inflammatory factors originating from the gut and carried in the lymph are responsible for the lung injury observed after T/HS. This study investigates whether the protective effect of amiloride against T/HS-induced lung injury was associated with decreased lymph toxicity and gut permeability.

METHODS

Male rats subjected to trauma (laparotomy) plus hemorrhagic shock (mean arterial pressure, 30 mm Hgx90 min) (T/HS) or trauma plus sham shock (T/SS) and treated with amiloride or its vehicle had their mesenteric lymph duct catheterized. Mesenteric lymph collected before and after shock was assayed for biologic activity on endothelial cells (cytotoxicity and permeability) and neutrophils (respiratory burst activity). Gut permeability was assessed by monitoring plasma concentrations of the fluorescent dye FITC-dextran after its injection into the ileum.

RESULTS

Amiloride administration reduced the capacity of post-shock mesenteric lymph to prime neutrophils for an increased respiratory burst. Amiloride failed to decrease the ability of mesenteric lymph to kill endothelial cells or increase their permeability. Amiloride decreased gut permeability.

CONCLUSIONS

The mechanisms of the lung protective effect of amiloride in rats undergoing T/HS may be secondary to decreased neutrophil activation, diminished gut permeability, or an effect on the end organ.

The Na+/H+ exchanger NHE1 in stress-induced signal transduction: implications for cell proliferation and cell death

The ubiquitous plasma membrane Na+/H+ exchanger NHE1 is highly conserved across vertebrate species and is extensively characterized as a major membrane transport mechanism in the regulation of cellular pH and volume. In recent years, the understanding of the role of NHE1 in regulating cell function has expanded from one of a household protein involved in ion homeostasis to that of a multifaceted regulator and/or modulator of a wide variety of cell functions. NHE1 plays pivotal roles in response to a number of important physiological stress conditions which, in addition to cell shrinkage and acidification, include hypoxia and mechanical stimuli, such as cell stretch. It has recently become apparent that NHE1-mediated modulation of, e.g., cell migration, morphology, proliferation, and death results not only from NHE1-mediated changes in pHi, cell volume, and/or [Na+]i, but also from direct protein-protein interactions with, e.g., ezrin/radixin/moesin (ERM) proteins and regulation of cellular signaling events, including the activity of mitogen-activated protein kinases (MAPKs) and Akt/protein kinase B (PKB). The aim of this review is to present and discuss new findings implicating NHE1 activation as a central signaling event activated by stress conditions and modulating cell proliferation and death. The pathophysiological importance of NHE1 in modulating the balance between cell proliferation and cell death in cancer and in ischemia/severe hypoxia will also be briefly addressed.

Amiloride combined with small-volume resuscitation with hypertonic saline is superior in ameliorating trauma-hemorrhagic shock-induced lung injury in rats to the administration of either agent alone

OBJECTIVE

Recognition of the limitations of standard crystalloid resuscitation has led to exploration for alternative resuscitation strategies that might better prevent the development of trauma-hemorrhage-induced organ dysfunction and systemic inflammation. Thus, the goal of this study was to compare the effects of two resuscitation strategies alone and in combination with that of standard resuscitation with Ringer's lactate. These two strategies were intravenous injection of amiloride, an inhibitor of Na/H exchange and epithelial Na channels, and resuscitation with hypertonic saline.

DESIGN

Prospective animal study with concurrent control.

SETTING

Small animal laboratory.

SUBJECTS

Adult male Sprague-Dawley rats.

INTERVENTIONS

Rats injected with amiloride or its vehicle were subjected to trauma-hemorrhagic shock (T/HS) or trauma sham-shock (T/SS) and resuscitated with Ringer's lactate or hypertonic saline. The T/HS model consisted of a laparotomy plus 90 mins of shock (mean arterial pressure 30 mm Hg). Three hours after the end of the shock or sham-shock period, lung permeability, lung histology, pulmonary neutrophil sequestration, neutrophil CD11b expression, gut injury, and red blood cell rigidification were assessed.

MEASUREMENTS AND MAIN RESULTS

Both amiloride and hypertonic saline reduced T/HS-induced pulmonary permeability and neutrophil sequestration, and coadministration of these two agents was more efficacious than administration of the individual agents. In contrast, whereas gut injury was attenuated by both amiloride and hypertonic saline, combined administration of amiloride and hypertonic saline failed to further protect the gut. Additionally, hypertonic saline reduced both neutrophil CD11b expression and red blood cell rigidification, whereas amiloride was without effect.

CONCLUSIONS

Combined administration of amiloride and small-volume resuscitation with hypertonic saline may be a strategy worthy of further evaluation in the therapy of shock-induced distant organ injury.

Signaling of short- and long-term regulation of intestinal epithelial type 1 Na+/H+ exchanger by interferon-gamma

The present study evaluated the effect of interferon-gamma (IFN-gamma) on intestinal Na+/H+ exchange (NHE) activity and the intracellular signaling pathways set into motion after IFN-gamma receptor activation. Caco-2 cells express endogenous NHE1, NHE2 and NHE3 proteins, as detected by immunoblotting. Short- (0.5 h) and long- (24 h) term exposure of Caco-2 cells to IFN-gamma resulted in a concentration-dependent decrease in NHE activity. Inhibition of NHE activity by IFN-gamma was absent in cariporide-treated cells, but not in cells treated with S-3226. The long-term exposure to IFN-gamma was accompanied by a 20% increase in surface NHE1 abundance and no changes in total NHE1 abundance. Inhibition of Raf1, mitogen-activated protein kinase kinase (MAPKK/MEK) and p38 MAPK with, respectively, GW 5074, PD 98059 and SB 203580 and downregulation of protein kinase C (PKC) with phorbol-12,13-dibutyrate (100 nM for 24 h) prevented inhibition of NHE activity by IFN-gamma (0.5 and 24 h exposure). The signal transducer and activator transcription factor 1 (STAT1) inhibitor epigallocatechin-3-gallate (EGCG) prevented inhibition of NHE activity by long- but not the short-term treatment with IFN-gamma. Treatment with IFN-gamma activated phospho-p38 MAPK, this effect being detected as early as 1 h, persisting over 3 h and decreasing after 24 h. IFN-gamma produced a sustained action of phospho-STAT1 that was prevented by EGCG and partially attenuated by SB 203580 and insensitive to downregulation of PKC. In conclusion, short- and long-term inhibition of NHE1 activity by IFN-gamma involves a complex signaling pathway that includes PKC activation and STAT1 phosphorylation, respectively, but is not accompanied by downregulation of NHE1.

Amiloride and the regulation of NF-kappaB: an unsung crosstalk and missing link between fluid dynamics and oxidative stress-related inflammation--controversy or pseudo-controversy?

Understanding the biophysics of fluid dynamics within the context of transcriptional regulation, mediated by nuclear factor (NF)-kappaB, is crucial to developing a consensus on the molecular basis of fluid mechanics and imbalance. Amiloride, an antikaliuretic-diuretic agent, has recently entered the realm of NF-kappaB as a key player in regulating the molecular association of fluid dynamics with inflammation and oxidative stress. With the identification of flanking regions encoding the amiloride-sensitive channels that are NF-kappaB-responsive, a new theme emerges which underlies the significance of this association. What is the role of NF-kappaB in regulating fluid mechanics-is it a physiologic or immunologic function? Conversely, amiloride is purported as a major regulator of this transcriptional pathway. It is the mainstream of this survey, therefore, to outline current advances on the biophysics and nature of the interaction existing between amiloride, amiloride-sensitive channels, and NF-kappaB, while searching for potential molecular mechanisms.

Disordered enterocyte signaling and intestinal barrier dysfunction in the pathogenesis of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the leading cause of death from gastrointestinal disease in neonates, and is characterized by the development of diffuse intestinal necrosis in the stressed, pre-term infant. Systemic stress causes a breakdown in the intestinal mucosal barrier, which leads to translocation of bacteria and endotoxin and the initiation of a signaling response within the enterocyte. This review summarizes recent evidence defining a clear role that defective enterocyte signaling plays in the pathogenesis of NEC through the following mechanisms: 1) The localized production of nitric oxide by villus enterocytes results in an increase in enterocyte apoptosis and impaired proliferation; 2) The translocation of endotoxin results in a PI3K-dependent activation of RhoA-GTPase within the enterocyte leading to decreased enterocyte migration and impaired restitution; 3) Dysregulated sodium-proton exchange within the enterocyte by endotoxin renders the enterocyte monolayer more susceptible to damage in the face of the acidic microenvironment characteristic of systemic sepsis; and 4) Endotoxin causes a p38-dependent release of the pro-inflammatory molecule COX-2 by the enterocyte, which potentiates the systemic inflammatory response. An understanding of the mechanisms by which disordered enterocyte signaling contributes to the pathogenesis of barrier failure and NEC--through these and other mechanisms--may lead to the identification of novel therapeutic approaches for this devastating disease.

Inhibitory effect of luteolin on TNF-α-induced IL-8 production in human colon epithelial cells

Interleukin (IL)-8 plays a central role in the initiation and maintenance of inflammatory responses in the inflammatory bowel disease. The proinflammatory cytokine-mediated production of IL-8 requires activation of various kinases, which leads to the IkappaB degradation and NF-kappaB activation. In this study, we investigated the role of luteolin, a major flavonoid of Lonicera japonica, on TNF-alpha-induced IL-8 production in human colonic epithelial cells. HT29 cells were stimulated with TNF-alpha in the presence or absence of luteolin. IL-8 production was measured by enzyme-linked immunosorbent assay (ELISA) and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, and the mitogen-activated protein kinases (MAPKs) activation and IkappaB degradation were determined by Western blot analysis. NF-kappaB activation was assessed by the electrophoretic motility shift assay (EMSA). Luteolin suppressed TNF-alpha-induced IL-8 production in dose-dependent manner. In addition, luteolin inhibited TNF-alpha-induced phosphorylation of p38 MAPK and extracellular-regulated kinases (ERK), IkappaB degradation, and NF-kappaB activation. These results suggest that luteolin has the inhibitory effects on TNF-alpha-induced IL-8 production in the intestinal epithelial cells through blockade in the phosphorylation of MAPKs, following IkappaB degradation and NF-kappaB activation.

Differential regulation of Na+/H+ exchange isoform activities by enteropathogenic E. coli in human intestinal epithelial cells

Enteropathogenic Escherichia coli (EPEC) is an important human intestinal foodborne pathogen associated with diarrhea, especially in infants and young children. Although EPEC produces characteristic attaching and effacing lesions and loss of microvilli, the pathophysiology of EPEC-associated diarrhea, particularly during early infection, remains elusive. The present studies were designed to examine the direct effects of EPEC infection on intestinal absorption via Na(+)/H(+) exchanger (NHE) isoforms. Caco-2 cells were infected with EPEC strain E2348/69 or nonpathogenic E. coli HB101 for a period of 60 to 120 min. Total NHE activity was significantly increased at 60 min, reaching approximately threefold increase after 90 min of EPEC infection. Similar findings were seen in HT-29 cells and T84 cells indicating that the response was not cell-line specific. Most surprising was the differential regulation of NHE2 and NHE3 by EPEC. Marked activation of NHE2 (300%) occurred, whereas significant inhibition ( approximately 50%) of NHE3 activity was induced. The activity of basolateral isoform NHE1 was also significantly increased in response to EPEC infection. Mutations that disrupted the type III secretion system (TTSS) ablated the effect of EPEC on the activity of both NHE2 and NHE3. These results suggest that EPEC, through a TTSS-dependent mechanism, exerts differential effects on NHE isoform activity in intestinal epithelial cells. Additionally, NHEs do not appear to play any role in EPEC-mediated inflammation, because the NHE inhibitors amiloride and 5-(N-ethyl-N-isopropyl)amiloride did not prevent EPEC-mediated IkappaBalpha degradation.

Endotoxin differentially modulates the basolateral and apical sodium/proton exchangers (NHE) in enterocytes

BACKGROUND

Maintenance of enterocyte activity during extracellular acidosis requires functional sodium/proton exchangers (NHE), which are present at both basolateral and apical surfaces. Necrotizing enterocolitis is characterized by systemic hypoperfusion, metabolic acidosis, and the apical to basolateral translocation of endotoxin (lipopolysaccharide [LPS]). We hypothesized that LPS differentially impairs NHE activity at the basolateral or apical domains of enterocytes, leading to cellular acidification, and explored the mechanisms involved.

METHODS

Experimental necrotizing enterocolitis (NEC) was induced in newborn rats using a combination of gavage feeds and hypoxia. NHE isoforms were assessed in primary and cultured enterocytes by Western blot analysis and by confocal microscopy in the presence or absence of LPS. NHE activity was detected by single-cell fluorescent ratiometric imaging with the use of the pH-sensitive dye 2', 7'-bis-(2carboxyethyl) -5-(and-6)-carboxyfluorescein.

RESULTS

In both NEC and control rats, NHE1 was basolateral and NHE3 was apical. A similar distribution was observed in polarized IEC-6 cells. LPS caused a dose-dependent reduction in basolateral NHE1 activity in IEC-6 cells, but had no effect on apical NHE3 activity. This effect could not be accounted for by reduced expression or impaired plasma membrane localization of NHE isoforms. Strikingly, LPS-mediated NHE1 impairment caused marked cytoplasmic acidification under conditions of extracellular acidosis, whereas functional NHE1 maintained cytoplasmic pH homeostasis in control cells.

CONCLUSIONS

LPS selectively impairs basolateral NHE1 but not apical NHE3, leading to cytoplasmic acidification during extracellular acidosis. This effect could mediate impaired enterocyte function after LPS translocation and suggests a mechanism leading to barrier disruption in NEC.

Acanthoic acid inhibits IL-8 production via MAPKs and NF-κB in a TNF-α-stimulated human intestinal epithelial cell line

BACKGROUND

Intestinal epithelial cells (IECs) can produce cytokines and chemokines that play an important role in the mucosal immune response. Regulation of this production is important to prevent inflammatory tissue damage. The root and stem barks of Acanthopanax species have been used as a tonic and sedative as well as in the treatment of rheumatism and diabetes. The aim of this study was to examine the inhibitory effect of acanthoic acid isolated from Acanthopanax koreanum (Araliaceae), on IL-8 production via mitogen-activated protein kinases (MAPKs) and nuclear factor-kappa B (NF-kappaB) in TNF-alpha-stimulated human colon epithelial cells.

METHODS

HT29 cells were stimulated with TNF-alpha in the presence or absence of acanthoic acid. IL-8 production was measured by enzyme-linked immunosorbent assay (ELISA) and reverse transcription-PCR (RT-PCR). MAPK activation and IkappaB/NF-kappaB expression were assessed by Western blot analysis. NF-kappaB activation was determined using immunofluorescence localization and electrophoretic mobility shift assay (EMSA).

RESULTS

Acanthoic acid suppressed TNF-alpha-induced IL-8 production in a dose-dependent manner. Furthermore, acanthoic acid inhibited TNF-alpha-induced MAPKs (p38, JNK1/2, and ERK1/2) activation, IkappaB degradation, NF-kappaB nuclear translocation, and NF-kappaB/DNA binding activity.

CONCLUSION

Acanthoic acid might inhibit TNF-alpha-mediated IL-8 production by blocking in both the MAPKs and NF-kappaB pathways in HT29 cells.

Disruption of the actin cytoskeleton results in nuclear factor‐κB activation and inflammatory mediator production in cultured human intestinal epithelial cells

The cytoskeleton in eukaryotic cells is composed of two major filament systems, the microtubule system and the actin cytoskeleton. The microtubule system has recently emerged as an important regulator of NF-kappaB function. However, the role that the actin microfilament system plays in controlling NF-kappaB activation is incompletely understood. In this study, we examined the effect of actin cytoskeleton disruption on NF-kappaB activation in human intestinal epithelial cells. Treatment of HT-29 or Caco-2 cells with the prototypic actin disrupting agents cytochalasin D or latrunculin B resulted in increased NF-kappaB DNA binding and NF-kappaB-dependent transcriptional activity. This NF-kappaB activation by cytochalasin D was secondary to an effect on IkappaB, because cytochalasin D-induced IkappaB degradation and the cytochalasin D-induced increase in NF-kappaB-dependent transcriptional activity was prevented by a dominant negative IkappaB mutant. Exposure of the cells to cytochalasins or latrunculin B increased gene expression and release of the NF-kappaB-dependent chemokines IL-8 and GRO-alpha. Cytochalasin D also activated p38 MAP kinase, which pathway contributed to the cytochalasin D-induced increase in IL-8 production. These results demonstrate that the actin cytoskeleton plays an important role in the regulation of NF-kappaB activation and inflammatory events in intestinal epithelial cells.

ERK Is Regulated by Sodium-Proton Exchanger in Rat Aortic Vascular Smooth Muscle Cells

The purposes of this study were to test 1) the relationship between two widely studied mitogenic effector pathways, and 2) the hypothesis that sodium-proton exchanger type 1 (NHE-1) is a regulator of extracellular signal-regulated protein kinase (ERK) activation in rat aortic smooth muscle (RASM) cells. Angiotensin II (Ang II) and 5-hydroxytryptamine (5-HT) stimulated both ERK and NHE-1 activities, with activation of NHE-1 preceding that of ERK. The concentration-response curves for 5-HT and Ang II were superimposable for both processes. Inhibition of NHE-1 with pharmacological agents or by isotonic replacement of sodium in the perfusate with choline or tetramethylammonium greatly attenuated ERK activation by 5-HT or Ang II. Similar maneuvers significantly attenuated 5-HT- or Ang II-mediated activation of MEK and Ras but not transphosphorylation of the epidermal growth factor (EGF) receptor. EGF receptor blockade attenuated ERK activation, but not NHE-1 activation by 5-HT and Ang II, suggesting that the EGF receptor and NHE-1 work in parallel to stimulate ERK activity in RASM cells, converging distal to the EGF receptor but at or above the level of Ras in the Ras-MEK-ERK pathway. Receptor-independent activation of NHE-1 by acute acid loading of RASM cells resulted in the rapid phosphorylation of ERK, which could be blocked by pharmacological inhibitors of NHE-1 or by isotonic replacement of sodium, closely linking the proton transport function of NHE-1 to ERK activation. These studies identify NHE as a new regulator of ERK activity in RASM cells.

Review article: mitogen-activated protein kinases in chronic intestinal inflammation - targeting ancient pathways to treat modern diseases

Conventional treatment of chronic inflammatory disorders, including inflammatory bowel diseases, employs broad-range anti-inflammatory drugs. In order to reduce the side-effects and increase the efficacy of treatment, several strategies have been developed in the last decade to interfere with intercellular and intracellular inflammatory signalling processes. The highly conserved mitogen-activated protein kinase pathways regulate most cellular processes, particularly defence mechanisms such as stress reactions and inflammation. In this review, we provide an overview of the current knowledge of the specificity and interconnection of mitogen-activated protein kinase pathways, their functions in the gut immune system and published and ongoing studies on the role of mitogen-activated protein kinases in inflammatory bowel disease. The development of mitogen-activated protein kinase inhibitors and their use for the therapy of inflammatory disorders is a paradigm of the successful bridging of the gap between basic research and clinical practice.

Pyrrolidinedithiocarbamate inhibits NF-kappaB activation and IL-8 production in intestinal epithelial cells

During inflammatory bowel disease and intestinal ischemia, epithelial cells of the gut mucosa produce various inflammatory mediators, including the chemokine interleukin (IL-8). This IL-8 produced by intestinal epithelial cells has recently been implicated as a contributory factor to the deleterious inflammatory process resulting in colitis during inflammatory bowel disease or multiple organ failure following shock and trauma. Recent evidence suggests that the transcription factor nuclear factor kappaB (NF-kappaB) is a central regulator of IL-8 gene expression. In the present paper we investigated the effect of pharmacological inhibition of NF-kappaB with pyrrolidinedithiocarbamate (PDTC) on IL-1beta-induced IL-8 production by the human intestinal epithelial cell line HT-29. Pretreatment of cells with PDTC (3-1000 microM) dose-dependently attenuated IL-8 production. Furthermore, PDTC (100 microM) suppressed the accumulation of IL-8 mRNA. PDTC inhibited the activation of NF-kappaB, because PDTC suppressed both NF-kappaB DNA binding and NF-kappaB-dependent transcriptional activity. Taken together, our data demonstrate that NF-kappaB inhibition with PDTC decreases IL-8 production by intestinal epithelial cells.

Inosine reduces inflammation and improves survival in a murine model of colitis

Inosine, a naturally occurring purine formed from the breakdown of adenosine, has recently been shown to exert powerful anti-inflammatory effects both in vivo and in vitro. This study evaluated inosine as a potential therapy for colitis. Colitis was induced in mice by the administration of dextran sulfate sodium (DSS). Oral treatment with inosine was begun either before the onset of colitis or as a posttreatment once colitis was established. Evaluation of colon damage and inflammation was determined grossly (body wt, rectal bleeding), histologically, and biochemically (colon levels of MPO, MDA, and cytokines). DSS-induced colitis significantly increased inflammatory cell infiltration into the colon. DSS-induced colitis also increased colon levels of lipid peroxidation, cytokines, and chemokines. Inosine protected the colon from DSS-induced inflammatory cell infiltration and lipid peroxidation. Inosine also partially reduced these parameters in an experimental model of established colitis. Thus inosine treatment may be a potential therapy in colitis.