Infective and inflammatory diarrhoea: mechanisms and opportunities for novel therapies

Up-regulation of NHE8 by somatostatin ameliorates the diarrhea symptom in infectious colitis mice model

Na⁺/H⁺ exchangers (NHEs) have been shown to be involved in regulating cell volume and maintaining fluid and electrolyte homeostasis. Pooled evidences have suggested that loss of Na⁺/H⁺ exchanger isoform 8 (NHE8) impairs intestinal mucosa. Whether NHE8 participates in the pathology of infectious colitis is still unknown. Our previous study demonstrated that somatostatin (SST) could stimulate the expression of intestinal NHE8 so as to facilitate Na⁺ absorption under normal condition. This study further explored whether NHE8 participates in the pathological processes of infectious colitis and the effects of SST on intestinal NHE8 expression in the setting of infectious colitis. Our data showed that NHE8 expression was reduced in Citrobacter rodentium (CR) infected mice. Up-regulation of NHE8 improved diarrhea symptom and mucosal damage induced by CR. In vitro, a similar observation was also seen in Enteropathogenic E. coli (EPEC) infected Caco-2 cells. Seglitide, a SST receptor (SSTR) 2 agonist, partly reversed the inhibiting action of EPEC on NHE8 expression, but SSTR5 agonist (L-817,818) had no effect on the expression of NHE8. Moreover, SST blocked the phosphorylation of p38 in EPEC-infected Caco-2 cells. Taken together, these results suggest that enhancement of intestinal NHE8 expression by SST could ameliorate the symptoms of mice with infectious colitis.

Pathophysiology of avian intestinal ion transport

The gut has great importance for the commercial success of poultry production. Numerous ion transporters, exchangers, and channels are present on both the apical and the basolateral membrane of intestinal epithelial cells, and their differential expression along the crypt-villus axis within the various intestinal segments ensures efficient intestinal absorption and effective barrier function. Recent studies have shown that intensive production systems, microbial exposure, and nutritional management significantly affect intestinal physiology and intestinal ion transport. Dysregulation of normal intestinal ion transport is manifested as diarrhoea, malabsorption, and intestinal inflammation resulting into poor production efficiency. This review discusses the basic mechanisms involved in avian intestinal ion transport and the impact of development during growth, nutritional and environmental alterations, and intestinal microbial infections on it. The effect of intestinal microbial infections on avian intestinal ion transport depends on factors such as host immunity, pathogen virulence, and the mucosal organisation of the particular intestinal segment.

Comparative pharmacokinetics of eight major bioactive components in normal and bacterial diarrhea mini-pigs after oral administration of Gegen Qinlian Decoction

Healthy animals are most widely used in current pharmacokinetic(PK) studies. However, neglecting the effects of specific diseases on drug absorption results in the PK parameters of those experiments not accurately reflecting in vivo drug concentration changes during treatment. In this study, an E. coli infective diarrheal minipig model was applied to explore the pharmacokinetics of Gegen Qinlian decoction (GQD). A simple and rapid ultrahigh performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method was developed to determine the concentrations of the eight GQD components in minipig plasma after intragastric administration of GQD. The PK parameters of the main GQD components in normal and model minipigs after oral administration of GQD were compared. There were statistically significant differences (p<0.05) in the pharmacokinetic parameters of Puerarin, Wogonin and Daidzein involving the AUC_0-t, Cmax, MRT_(0-t), t_1/2z between normal and model minipigs. Results showed that bacterial diarrhea had a great impact on the biological availability of the main ingredients in GQD. More importantly, the results obtained suggest that the bacterial diarrheal minipig model can be successfully applied in PK studies and may be used in other PK studies of drugs targeting intestinal disease.

Altered Prostasin (CAP1/Prss8) Expression Favors Inflammation and Tissue Remodeling in DSS-induced Colitis

BACKGROUND

Inflammatory bowel diseases (IBD) including ulcerative colitis and Crohn's disease are diseases with impaired epithelial barrier function. We aimed to investigate whether mutated prostasin and thus, reduced colonic epithelial sodium channel activity predisposes to develop an experimentally dextran sodium sulfate (DSS)-induced colitis.

METHODS

Wildtype, heterozygous (fr/+), and homozygous (fr/fr) prostasin-mutant rats were treated 7 days with DSS followed by 7 days of recovery and analyzed with respect to histology, clinicopathological parameters, inflammatory marker mRNA transcript expression, and sodium transporter protein expression.

RESULTS

In this study, a more detailed analysis on rat fr/fr colons revealed reduced numbers of crypt and goblet cells, and local angiodysplasia, as compared with heterozygous (fr/+) and wildtype littermates. Following 2% DSS treatment for 7 days followed by 7 days recovery, fr/fr animals lost body weight, and reached maximal diarrhea score and highest disease activity after only 3 days, and strongly increased cytokine levels. The histology score significantly increased in all groups, but fr/fr colons further displayed pronounced histological alterations with near absence of goblet cells, rearrangement of the lamina propria, and presence of neutrophils, eosinophils, and macrophages. Additionally, fr/fr colons showed ulcerations and edemas that were absent in fr/+ and wildtype littermates. Following recovery, fr/fr rats reached, although significantly delayed, near-normal diarrhea score and disease activity, but exhibited severe architectural remodeling, despite unchanged sodium transporter protein expression.

CONCLUSIONS

In summary, our results demonstrate a protective role of colonic prostasin expression against experimental colitis, and thus represent a susceptibility gene in the development of inflammatory bowel disease.

Lactobacillus acidophilus counteracts inhibition of NHE3 and DRA expression and alleviates diarrheal phenotype in mice infected with Citrobacter rodentium

Impaired absorption of electrolytes is a hallmark of diarrhea associated with inflammation or enteric infections. Intestinal epithelial luminal membrane NHE3 (Na⁺/H⁺ exchanger 3) and DRA (Down-Regulated in Adenoma; Cl^-/HCO₃^- exchanger) play key roles in mediating electroneutral NaCl absorption. We have previously shown decreased NHE3 and DRA function in response to short-term infection with enteropathogenic E coli (EPEC), a diarrheal pathogen. Recent studies have also shown substantial downregulation of DRA expression in a diarrheal model of infection with Citrobacter rodentium, the mouse counterpart of EPEC. Since our previous studies showed that the probiotic Lactobacillus acidophilus (LA) increased DRA and NHE3 function and expression and conferred protective effects in experimental colitis, we sought to evaluate the efficacy of LA in counteracting NHE3 and DRA inhibition and ameliorating diarrhea in a model of C rodentium infection. FVB/N mice challenged with C rodentium [1 × 10⁹ colony-forming units (CFU)] with or without administration of live LA (3 × 10⁹ CFU) were assessed for NHE3 and DRA mRNA and protein expression, mRNA levels of carbonic anhydrase, diarrheal phenotype (assessed by colonic weight-to-length ratio), myeloperoxidase activity, and proinflammatory cytokines. LA counteracted C rodentium-induced inhibition of colonic DRA, NHE3, and carbonic anhydrase I and IV expression and attenuated diarrheal phenotype and MPO activity. Furthermore, LA completely blocked C rodentium induction of IL-1β, IFN-γ, and CXCL1 mRNA and C rodentium-induced STAT3 phosphorylation. In conclusion, our data provide mechanistic insights into antidiarrheal effects of LA in a model of infectious diarrhea and colitis.

The weaned pig as a model for Doxorubicin-induced mucositis

BACKGROUND

Chemotherapy-induced mucositis (CIM) complicates cancer therapy and limits maximum tolerated doses and efficacy. Rodent models do not reproducibly mimic clinical CIM, so alternative models are needed.

METHODS

CIM severity was assessed after weaned pigs were treated with doxorubicin (5 and 3.75 mg/kg) using clinical observations, laboratory parameters and gastrointestinal structure and functions. Bovine colostrum was provided as an experimental intervention to the pigs treated receiving the 3.75 mg/kg dose.

RESULTS

Doxorubin at 3.75 mg/kg decreased food intake and weight gain (p < 0.05) and caused diarrhea and vomiting that coincided with damage to the small intestine mucosa based on histological scoring (p < 0.05). It resulted in higher serum TNF-α concentrations, increased chloride secretion and reduced brush border membrane disaccharidase activities and carrier-mediated glucose uptake (all p < 0.05). The gastrointestinal damage and dysfunction resemble the clinical and laboratory features of CIM in humans; these can be partially prevented by providing cow colostrum.

CONCLUSION

The weaned pig is a relevant large animal for studying CIM and evaluating existing and experimental interventions for mucositis.

Probiotic Bifidobacterium species stimulate human SLC26A3 gene function and expression in intestinal epithelial cells

SLC26A3, or downregulated in adenoma (DRA), plays a major role in mediating Cl(-) absorption in the mammalian intestine. Disturbances in DRA function and expression have been implicated in intestinal disorders such as congenital Cl(-) diarrhea and gut inflammation. We previously showed that an increase in DRA function and expression by Lactobacillus acidophilus and its culture supernatant (CS) might underlie antidiarrheal effects of this probiotic strain. However, the effects of Bifidobacterium species, important inhabitants of the human colon, on intestinal Cl(-)/HCO3 (-) exchange activity are not known. Our current results demonstrate that CS derived from Bifidobacterium breve, Bifidobacterium infantis, and Bifidobacterium bifidum increased anion exchange activity in Caco-2 cells (∼1.8- to 2.4-fold). Consistent with the increase in DRA function, CS also increased the protein, as well as the mRNA, level of DRA (but not putative anion transporter 1). CS of all three Bifidobacterium sp. increased DRA promoter activity (-1,183/+114 bp) in Caco-2 cells (1.5- to 1.8-fold). Furthermore, the increase in DRA mRNA expression by CS of B. breve and B. infantis was blocked in the presence of the transcription inhibitor actinomycin D (5 μM) and the ERK1/2 MAPK pathway inhibitor U0126 (10 μM). Administration of live B. breve, B. infantis, and B. bifidum by oral gavage to mice for 24 h increased DRA mRNA and protein levels in the colon. These data demonstrate an upregulation of DRA via activation of the ERK1/2 pathway that may underlie potential antidiarrheal effects of Bifidobacterium sp.

Potential for developing purinergic drugs for gastrointestinal diseases

Treatments for inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), functional dyspepsia, or motility disorders are not adequate, and purinergic drugs offer exciting new possibilities. Gastrointestinal symptoms that could be targeted for therapy include visceral pain, inflammatory pain, dysmotility, constipation, and diarrhea. The focus of this review is on the potential for developing purinergic drugs for clinical trials to treat gastrointestinal symptoms. Purinergic receptors are divided into adenosine P1 (A(1), A(2A), A(2B), A(3)), ionotropic ATP-gated P2X ion channel (P2X(1-7)), or metabotropic P2Y(1,2,4,6,11-14) receptors. There is good experimental evidence for targeting A(2A), A(2B), A(3), P2X(7), and P2X(3) receptors or increasing endogenous adenosine levels to treat IBD, inflammatory pain, IBS/visceral pain, inflammatory diarrhea, and motility disorders. Purine genes are also potential biomarkers of disease. Advances in medicinal chemistry have an accelerated pace toward clinical trials: Methotrexate and sulfasalazine, used to treat IBD, act by stimulating CD73-dependent adenosine production. ATP protects against NSAID-induced enteropathy and has pain-relieving properties in humans. A P2X(7)R antagonist AZD9056 is in clinical trials for Crohn's disease. A(3) adenosine receptor drugs target inflammatory diseases (e.g., CF101, CF102). Dipyridamole, a nucleoside uptake inhibitor, is in trials for endotoxemia. Drugs for pain in clinical trials include P2X(3)/P2X(2/3) (AF-219) and P2X(7) (GSK1482160) antagonists and A(1) (GW493838) or A(2A) (BVT.115959) agonists. Iberogast is a phytopharmacon targeting purine mechanisms with efficacy in IBS and functional dyspepsia. Purinergic drugs have excellent safety/efficacy profile for prospective clinical trials in IBD, IBS, functional dyspepsia, and inflammatory diarrhea. Genetic polymorphisms and caffeine consumption may affect susceptibility to treatment. Further studies in animals can clarify mechanisms and test new generation drugs. Finally, there is still a huge gap in our knowledge of human pathophysiology of purinergic signaling.

Murine neonates infected with Yersinia enterocolitica develop rapid and robust proinflammatory responses in intestinal lymphoid tissues

Neonatal animals are generally very susceptible to infection with bacterial pathogens. However, we recently reported that neonatal mice are highly resistant to orogastric infection with Yersinia enterocolitica. Here, we show that proinflammatory responses greatly exceeding those in adults arise very rapidly in the mesenteric lymph nodes (MLN) of neonates. High-level induction of proinflammatory gene expression occurred in the neonatal MLN as early as 18 h postinfection. Marked innate phagocyte recruitment was subsequently detected at 24 h postinfection. Enzyme-linked immunosorbent spot assay (ELISPOT) analyses indicated that enhanced inflammation in neonatal MLN is contributed to, in part, by an increased frequency of proinflammatory cytokine-secreting cells. Moreover, both CD11b(+) and CD11b(-) cell populations appeared to play a role in proinflammatory gene expression. The level of inflammation in neonatal MLN was also dependent on key bacterial components. Y. enterocolitica lacking the virulence plasmid failed to induce innate phagocyte recruitment. In contrast, tumor necrosis factor alpha (TNF-α) protein expression and neutrophil recruitment were strikingly higher in neonatal MLN after infection with a yopP-deficient strain than with wild-type Y. enterocolitica, whereas only modest increases occurred in adults. This hyperinflammatory response was associated with greater colonization of the spleen and higher mortality in neonates, while there was no difference in mortality among adults. This model highlights the dynamic levels of inflammation in the intestinal lymphoid tissues and reveals the protective (wild-type strain) versus harmful (yopP-deficient strain) consequences of inflammation in neonates. Moreover, these results reveal that the neonatal intestinal lymphoid tissues have great potential to rapidly mobilize innate components in response to infection with bacterial enteropathogens.

Fluid and electrolyte secretion in the inflamed gut: novel targets for treatment of inflammation-induced diarrhea

Diarrheal disease can occur in the context of both inflammatory and infectious challenges. Inflammation can result in changes in ion transporter expression or simply mislocalization of the protein. In addition to development of diarrhea, an altered secretory state can lead to changes in mucus secretion and luminal pH. Bacterial infection can lead to subversion of host cell signaling, leading to transporter mislocalization and hyposecretion, promoting bacterial colonization. Novel therapeutic strategies are currently being developed to ameliorate transporter defects in the setting of inflammation or bacterial infection including, for example, administration of probiotics and fecal microbiota transplantation. This review will highlight recent findings in the literature detailing these aspects of ion transport in the inflamed gut.