Regional intestinal adaptations in Na+,K+-ATPase in experimental colitis and the contrasting effects of interferon-gamma

The role of salt-inducible kinases on the modulation of renal and intestinal Na+,K+-ATPase activity during short- and long-term high-salt intake

Type 1 salt-inducible kinases (SIK1) has been shown to act as a mediator during the cellular adaptation to variations in intracellular sodium in a variety of cell types. Type 2 SIK (SIK2) modulates various biological functions and acts as a signal transmitter in various pathways. To evaluate the role of both SIK isoforms in renal and intestinal Na+,K+-ATPase (NKA) activity, we made use of constitutive sik1-/- (SIK1-KO), sik2-/- (SIK2-KO), double sik1-/-sik2-/- (double SIK1*2-KO) knockout and wild-type (WT) mice challenged to a standard (0.3% NaCl) or chronic high-salt (HS, 8% NaCl) diet intake for 48 h or 12 weeks. Long-term HS intake in WT was accompanied by 2-fold increase in jejunal NKA activity and slight (~30% reduction) decreases in NKA in the ileum and cecum; none of these changes was accompanied by changes in the expression of α1-NKA. The ablation of SIK1 and SIK2 prevented the marked increase in jejunal NKA activity following the long-term HS intake. The ablation of SIK1 and SIK2 in mice on a long-term HS intake impacted differently in the ileum and cecum. The most interesting finding is that in SIK2-KO mice marked reductions in NKA activity were observed in the ileum and cecum when compared to WT mice, both on normal and long-term HS intake. In summary, SIK1 or SIK2 ablation on chronic high-salt intake is accompanied by modulation of NKA along the intestinal tract, which differ from those after an acute high-salt intake, and this may represent an absorptive compensatory mechanism to keep electrolyte homeostasis.

Pathophysiology of IBD associated diarrhea

Inflammatory bowel diseases broadly categorized into Crohn's disease (CD) and ulcerative colitis (UC), are chronic inflammatory disorders of the gastrointestinal tract with increasing prevalence worldwide. The etiology of the disease is complex and involves a combination of genetic, environmental, immunological and gut microbial factors. Recurring and bloody diarrhea is the most prevalent and debilitating symptom in IBD. The pathogenesis of IBD-associated diarrhea is multifactorial and is essentially an outcome of mucosal damage caused by persistent inflammation resulting in dysregulated intestinal ion transport, impaired epithelial barrier function and increased accessibility of the pathogens to the intestinal mucosa. Altered expression and/or function of epithelial ion transporters and channels is the principle cause of electrolyte retention and water accumulation in the intestinal lumen leading to diarrhea in IBD. Aberrant barrier function further contributes to diarrhea via leak-flux mechanism. Mucosal penetration of enteric pathogens promotes dysbiosis and exacerbates the underlying immune system further perpetuating IBD associated-tissue damage and diarrhea. Here, we review the mechanisms of impaired ion transport and loss of epithelial barrier function contributing to diarrhea associated with IBD.

Potential usefulness of methyl gallate in the treatment of experimental colitis

Methyl gallate is a gallotannin widely distributed in nature. Previous studies have demonstrated its antioxidant, anti-inflammatory, antimicrobial and anti-tumor activities. In the present study, the activity of methyl gallate on experimental models of inflammatory bowel disease has been investigated. Experimental colitis was induced in Sprague-Dawley rats through the intracolonic instillation of an acetic acid solution (2 mL, 4% v/v). Methyl gallate (100 and 300 mg/kg, p.o.) and the reference drug mesalazine (100 mg/kg, p.o.) were tested. Methyl gallate induced a significant reduction in the colon weight/length ratio and macroscopic lesion score. Besides, the malondialdehyde content and the GSSG/GSH ratio were remarkably decreased. Furthermore, the administration of methyl gallate reduced the expression of COX₂, IL-6, TNFα and the severity of microscopic tissue damage induced by acetic acid, while the mean goblet cell density was significantly higher in both the group treated with methyl gallate and the one treated with mesalazine, in comparison with untreated animals. The Na⁺K⁺ATPase pump activity was recovered in treated groups (control: 827.2 ± 59.6, colitis: 311.6 ± 54.8, methyl gallate 100 mg/kg: 642.2 ± 175.0, methyl gallate 300 mg/kg: 809.7 ± 100.6, mesalazine: 525.3 ± 81.7). Methyl gallate was also found to induce a significant reduction in the castor oil-induced intestinal motility in Swiss mice, decreasing the peristalsis by 74.5 and 58.82% at 100 and 300 mg/kg p.o., respectively. This compound also antagonized the jejunum contractions induced by Ach and CaCl₂. This study demonstrates that methyl gallate exerts beneficial effects in a preclinical model of intestinal disorders.

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.

Amine neurotransmitters, inflammation and epithelial sodium transport

NEW FINDINGS

What is the topic of this review? The present work reviews the roles of renal and intestinal dopamine and 5-HT in the maintenance of fluid and electrolyte homeostasis. The role of inflammatory agents at the intestinal level that affect fluid and electrolyte homeostasis is also addressed. What advances does it highlight? General mechanisms of epithelial cell ion transport in the gastrointestinal tract and kidney share considerable similarities, particularly with regard to basolateral Na(+) ,K(+-) ATPase as a driving force for the movement of numerous substrates across the cell membrane. The physiological importance of the renal actions of monoamines (dopamine, noradrenaline and 5-HT) mainly depends on the sources of the amines in the kidney and on their availability to activate the amine-specific receptors. Dopamine and 5-HT are also relatively abundant in the mucosal cell layer of the intestine, and recent evidence suggests their physiological relevance in regulating electrolyte transport. The gastrointestinal tract can be an important site for the loss of water and electrolytes, in the presence of intestinal inflammation. General mechanisms of epithelial cell ion transport in the gastrointestinal tract and kidney share considerable similarities with regard to basolateral Na(+) ,K(+) -ATPase as a driving force for the movement of numerous substrates across the cell membrane. The present work reviews the roles of renal and intestinal dopamine and 5-HT in the maintenance of fluid and electrolyte homeostasis. The role of inflammatory agents at the intestinal level that affect fluid and electrolyte homeostasis is also addressed.

Basolateral ion transporters involved in colonic epithelial electrolyte absorption, anion secretion and cellular homeostasis

Electrolyte transporters located in the basolateral membrane of the colonic epithelium are increasingly appreciated as elaborately regulated components of specific transport functions and cellular homeostasis: During electrolyte absorption, Na(+) /K(+) ATPase, Cl⁻ conductance, Cl⁻/HCO₃⁻ exchange, K(+) /Cl⁻ cotransport and K(+) channels are candidates for basolateral Na(+) , Cl⁻ and K(+) extrusion. The process of colonic anion secretion involves basolateral Na(+) /K(+) /2Cl⁻ , and probably also Na(+) /HCO₃⁻ cotransport, as well as Na(+) /K(+) ATPase and K(+) channels to supply substrate, stabilize the membrane potential and generate driving force respectively. Together with a multitude of additional transport systems, Na(+) /H(+) exchange and Na(+) /HCO₃⁻ cotransport have been implicated in colonocyte pH(i) and volume homeostasis. The purpose of this article is to summarize recently gathered information on the molecular identity, function and regulation of the involved basolateral transport systems in native tissue. Furthermore, we discuss how these findings can help to integrate these systems into the transport function and the cellular homoeostasis of colonic epithelial cells. Finally, disturbances of basolateral electrolyte transport during disease states such as mucosal inflammation will be reviewed.

Montelukast, a selective cysteinyl leukotriene receptor 1 antagonist, reduces cerulein-induced pancreatic injury in rats

OBJECTIVES

This study was designed to evaluate the protective effect of the cysteinyl leukotriene receptor antagonist montelukast against pancreatic injury during acute pancreatitis.

METHODS

Acute pancreatitis was induced in rats by 20-μg/kg (intraperitoneal) cerulein given at 1-hour intervals within 4 hours. Montelukast was administered intraperitoneally at a dose of 10 mg/kg 15 minutes before the first cerulein injection. Six hours after the cerulein or saline injections, the animals were killed by decapitation. Blood samples were collected to analyze amylase, lipase, and the proinflammatory cytokines tumor necrosis factor α and interleukin 1β. Pancreas tissues were taken for the determination of tissue glutathione and malondialdehyde levels and Na,K-adenosine triphosphatase and myeloperoxidase activities. The extent of tissue injury was analyzed microscopically.

RESULTS

Acute pancreatitis caused significant decreases in tissue glutathione level and Na,K-adenosine triphosphatase activity, which were accompanied with significant increases in the pancreatic malondialdehyde level, myeloperoxidase activity, and plasma cytokine level. On the other hand, montelukast treatment reversed all these biochemical indices and histopathological alterations that were induced by cerulein.

CONCLUSIONS

These results suggest that cysteinyl leukotrienes may be involved in the pathogenesis of acute pancreatitis and that the cysteinyl leukotriene receptor antagonist, montelukast, might be of therapeutic value for treatment of acute pancreatitis.

Protective Effects of Proanthocyanidin on Cerulein-induced Acute Pancreatic Inflammation in Rats

Background

The aim of this study was to assess the possible protective effect of proanthocyanidin against cerulein-induced acute pancreatic inflammation (AP) and oxidative injury.

Methods

Sprague-Dawley rats were pretreated with proanthocyanidine (100 mg/kg, orally) or saline 15 min before cerulein was given by 20 µg/kg subcutaneously at 1-h intervals within 4 hours. Six hours after cerulein or saline injections, the animals were killed by decapitation. Blood samples were collected to analyze amylase, lipase, and proinflammatory cytokines (TNF-α and IL-1b). Pancreas tissues were taken for the determination of tissue glutathione (GSH) and malondialdehyde (MDA) levels, Na⁺, K⁺-ATPase and myeloperoxidase (MPO) activities. Formation of reactive oxygen species in pancreatic tissue samples was monitored by using chemiluminescence (CL) technique with luminol and lucigenin probes, while the extent of tissue injury was analyzed microscopically.

Results

Acute pancreatitis caused a significant decrease in tissue GSH level and Na⁺, K⁺-ATPase activity, which was accompanied with significant increases in the pancreatic MDA, luminol and lucigenin chemiluminescences (CL) levels and MPO activity. Similarly TNF-α and IL-1β levels were elevated in the pancreatic group as compared to control group. On the other hand, proanthocyanidin treatment reversed all these biochemical indices, as well as histopathological alterations that were induced by cerulein.

Conclusions

Proanthocyanidine can ameliorate pancreatic injury induced by cerulein in rats, this result suggests that proanthocyanidin may have utility in treating acute pancreatititis.

Interferon-γ-induced STAT1-mediated membrane retention of NHE1 and associated proteins ezrin, radixin and moesin in HT-29 cells

This study evaluated the effect of interferon-gamma (IFN-gamma) upon the function and expression of type 1 Na(+)/H+ exchanger (NHE1) in human intestinal epithelial HT-29 cells, namely that concerning the abundance of surface NHE1 and NHE1 binding to the ezrin, radixin and moesin (ERM) family of proteins. HT-29 cells express endogenous NHE1 and the ERM family of proteins that retain the localization of NHE1 in the membrane. Long-term exposure (24 h) of HT-29 cells to IFN-gamma resulted in a concentration-dependent decrease in NHE1 activity. Inhibition of NHE1 activity by IFN-gamma was absent after pretreatment with cariporide. The long-term exposure to IFN-gamma was accompanied by increase in surface NHE1 and ERM abundance and no changes in total NHE1 and ERM abundance. Inhibition of signal transducer and activator transcription factor 1 (STAT1) with epigallocatechin-3-gallate (EGCG) prevented the inhibitory effect of IFN-gamma. Treatment with IFN-gamma activated phospho-STAT1 was markedly attenuated by EGCG. The IFN-gamma-induced increase in surface NHE1 and ERM abundance was prevented by EGCG. In conclusion, long-term inhibition of NHE1 activity by IFN-gamma involves STAT1 phosphorylation and is accompanied by increased abundance of surface NHE1 and the NHE1 membrane anchoring ERM proteins.