Tumor necrosis factor-α and interferon-γ increase PepT1 expression and activity in the human colon carcinoma cell line Caco-2/bbe and in mouse intestine

Extracellular Vesicles of the Probiotic Escherichia coli Nissle 1917 Reduce PepT1 Levels in IL-1β-Treated Caco-2 Cells via Upregulation of miR-193a-3p

PepT1, a proton-coupled oligopeptide transporter, is crucial for intestinal homeostasis. It is mainly expressed in small intestine enterocytes, facilitating the absorption of di/tri-peptides from dietary proteins. In the colon, PepT1 expression is minimal to prevent excessive responses to proinflammatory peptides from the gut microbiota. However, increased colonic PepT1 is linked to chronic inflammatory diseases and colitis-associated cancer. Despite promising results from animal studies on the benefits of extracellular vesicles (EVs) from beneficial gut commensals in treating IBD, applying probiotic EVs as a postbiotic strategy in humans requires a thorough understanding of their mechanisms. Here, we investigate the potential of EVs of the probiotic Nissle 1917 (EcN) and the commensal EcoR12 in preventing altered PepT1 expression under inflammatory conditions, using an interleukin (IL)-1-induced inflammation model in Caco-2 cells. The effects are evaluated by analyzing the expression of PepT1 (mRNA and protein) and miR-193a-3p and miR-92b, which regulate, respectively, PepT1 mRNA translation and degradation. The influence of microbiota EVs on PepT1 expression is also analyzed in the presence of bacterial peptides that are natural substrates of colonic PepT1 to clarify how the regulatory mechanisms function under both physiological and pathological conditions. The main finding is that EcN EVs significantly decreases PepT1 protein via upregulation of miR-193a-3p. Importantly, this regulatory effect is strain-specific and only activates in cells exposed to IL-1β, suggesting that EcN EVs does not control PepT1 expression under basal conditions but can play a pivotal role in response to inflammation as a stressor. By this mechanism, EcN EVs may reduce inflammation in response to microbiota in chronic intestinal disorders by limiting the uptake of bacterial proinflammatory peptides.

Salmonella Typhimurium Infection Reduces the Ascorbic Acid Uptake in the Intestine

Salmonella Typhimurium infection of the gastrointestinal tract leads to damage that compromises the integrity of the intestinal epithelium and results in enterocolitis and inflammation. Salmonella infection promotes the expression of inflammasome NLRP3, leading to activation and release of proinflammatory cytokines such as IL-1β, and the infected host often displays altered nutrient levels. To date, the effect of Salmonella infection and proinflammatory cytokine IL-1β on the intestinal uptake of ascorbic acid (AA) is unknown. Our results revealed a marked decrease in the rate of AA uptake in mouse jejunum infected with Salmonella wild type (WT). However, the nonpathogenic mutant (Δ invA Δ spiB) strain did not affect AA uptake. The decrease in AA uptake due to Salmonella WT infection is accompanied by significantly lower expression of mouse (m)SVCT1 protein, mRNA, and hnRNA levels. NLRP3 and IL-1β expression levels were markedly increased in Salmonella-infected mouse jejunum. IL-1β-exposed Caco-2 cells displayed marked inhibition in AA uptake and significantly decreased hSVCT1 expression at both protein and mRNA levels. Furthermore, the activity of the SLC23A1 promoter was significantly inhibited by IL-1β exposure. In addition, GRHPR (a known SVCT1 interactor) protein and mRNA expression levels were significantly reduced in Salmonella-infected mouse jejunum. These results indicate that Salmonella infection inhibits AA absorption in mouse jejunum and IL-1β-exposed Caco-2 cells. The observed inhibitory effect may partially be mediated through transcriptional mechanisms.

Tumor necrosis factor α impedes colonic thiamin pyrophosphate and free thiamin uptake: involvement of JNK/ERK1/2-mediated pathways

The aim of this study was to examine the effect of TNFα (i.e., a predominant proinflammatory cytokine produced during chronic gut inflammation) on colonic uptake of thiamin pyrophosphate (TPP) and free thiamin, forms of vitamin B1 that are produced by the gut microbiota and are absorbed via distinct carrier-mediated systems. We utilized human-derived colonic epithelial CCD841 and NCM460 cells, human differentiated colonoid monolayers, and mouse intact colonic tissue preparations together with an array of cellular/molecular approaches in our investigation. The results showed that exposure of colonic epithelial cells to TNFα leads to a significant inhibition in TPP and free thiamin uptake. This inhibition was associated with: 1) a significant suppression in the level of expression of the colonic TPP transporter (cTPPT; encoded by SLC44A4), as well as thiamin transporters-1 & 2 (THTR-1 & -2; encoded by SLC19A2 & SLC19A3, respectively); 2) marked inhibition in activity of the SLC44A4, SLC19A2, and SLC19A3 promoters; and 3) significant suppression in level of expression of nuclear factors that are needed for activity of these promoters (i.e., CREB-1, Elf-3, NF-1A, SP-1). Furthermore, the inhibitory effects were found to be mediated via JNK and ERK1/2 signaling pathways. We also examined the level of expression of cTPPT and THTR-1 & -2 in colonic tissues of patients with active ulcerative colitis and found the levels to be significantly lower than in healthy controls. These findings demonstrate that exposure of colonocytes to TNFα suppresses TPP and free thiamin uptake at the transcriptional level via JNK- and Erk1/2-mediated pathways.

Gastrointestinal dynamics, immune response, and nutrient digestibility of weanling pigs fed diets supplemented with enzymatically treated yeast1

The objective of this trial was to investigate the effect of enzymatically treated yeast (ETY) on the growth performance, nutrient digestibility, immune response, and gut health of weanling pigs. A total of 192 weanling pigs (6.0 ± 1.04 kg) were allocated to 4 corn and soybean-based diets with increasing concentrations of ETY (0, 1, 2, or 4 g/kg) for a 43-d trial. There were 8 replicate pens (4 replicate pens per sex) and 6 pigs per replicate. The experiment was set up as a randomized complete block design with body weight used as a blocking factor. Pigs had ad libitum access to water and diets for the duration of the study. There was no effect of ETY supplementation on the growth performance indices of weanling pigs. At day 14, there was a quadratic decrease (P < 0.05) in the apparent total tract digestibility (ATTD) of acid detergent fiber (ADF). At day 28, there was a linear increase (P < 0.05) in the ATTD of neutral detergent fiber and a quadratic decrease (P < 0.05) in the ATTD of ADF. On day 14, there was a linear increase (P < 0.05) in serum catalase activity with ETY supplementation. There was a linear increase (P < 0.01) in the gene expression of glutathione peroxidase-4 in the ileal mucosa of pigs. Increasing dietary ETY supplementation linearly decreased (P < 0.05) the gene expression of ileal peptide transporter 1. There was a tendency for a quadratic effect (P = 0.07) in the ileal villus height to crypt depth ratio with ETY supplementation. In addition, there was a tendency for a linear increase (P = 0.06) in ileal digesta butyrate with ETY supplementation. In conclusion, the current study demonstrated that dietary ETY supplementation could partly ameliorate the deleterious effects of post-weaning stress by enhancing the antioxidative status of weanling pigs. However, prolonged supplementation of ETY may be needed to see its effect on growth performance.

Expression, Regulation, and Role of an Oligopeptide Transporter: PEPT1 in Tumors

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PEPT1 is a vital member of the proton-dependent oligopeptide transporters family (POTs). Many studies have confirmed that PEPT1 plays a critical role in the absorption of dipeptides, tripeptides, and pseudopeptides in the intestinal tract. In recent years, several studies have found that PEPT1 is highly expressed in malignant tumor tissues and cells. The abnormal expression of PEPT1 in tumors may be closely related to the progress of tumors, and hence, could be considered as a potential molecular biomarker for the diagnosis, treatment, and prognosis in malignant tumors. Furthermore, PEPT1 can be used to mediate the targeted delivery of anti-tumor drugs. Herein, the expression, regulation, and role of PEPT1 in tumors in recent years have been reviewed.

Painful interactions: Microbial compounds and visceral pain

Visceral pain, characterized by abdominal discomfort, originates from organs in the abdominal cavity and is a characteristic symptom in patients suffering from irritable bowel syndrome, vulvodynia or interstitial cystitis. Most organs in which visceral pain originates are in contact with the external milieu and continuously exposed to microbes. In order to maintain homeostasis and prevent infections, the immune- and nervous system in these organs cooperate to sense and eliminate (harmful) microbes. Recognition of microbial components or products by receptors expressed on cells from the immune and nervous system can activate immune responses but may also cause pain. We review the microbial compounds and their receptors that could be involved in visceral pain development.

GLUT12 expression and regulation in murine small intestine and human Caco-2 cells

GLUT12 was cloned from the mammary cancer cell line MCF-7, but its physiological role still needs to be elucidated. To gain more knowledge of GLUT12 function in the intestine, we investigated GLUT12 subcellular localization in the small intestine and its regulation by sugars, hormones, and intracellular mediators in Caco-2 cells and mice. Immunohistochemical methods were used to determine GLUT12 subcellular localization in human and murine small intestine. Brush border membrane vesicles were isolated for western blot analyses. Functional studies were performed in Caco-2 cells by measuring α-methyl-d-glucose (αMG) uptake in the absence of sodium. GLUT12 is located in the apical cytoplasm, below the brush border membrane, and in the perinuclear region of murine and human enterocytes. In Caco-2 cells, GLUT12 translocation to the apical membrane and α-methyl- d-glucose uptake by the transporter are stimulated by protons, glucose, insulin, tumor necrosis factor-α (TNF-α), protein kinase C, and AMP-activated protein kinase. In contrast, hypoxia decreases GLUT12 expression in the apical membrane. Upregulation of TNF-α and hypoxia-inducible factor-1α ( HIF-1α) genes is found in the jejunal mucosa of diet-induced obese mice. In these animals, GLUT12 expression in the brush border membrane is slightly decreased compared with lean animals. Moreover, an intraperitoneal injection of insulin does not induce GLUT12 translocation to the membrane, as it occurs in lean animals. GLUT12 rapid translocation to the enterocytes' apical membrane in response to glucose and insulin could be related to GLUT12 participation in sugar absorption during postprandial periods. In obesity, in which insulin sensitivity is reduced, the contribution of GLUT12 to sugar absorption is affected.

Inhibitory Potency of Marketed Drugs for Ulcerative Colitis and Crohn's Disease on PEPT1

We investigate the inhibitory effect of marketed drugs for treatment of inflammatory bowel disease (IBD) such as ulcerative colitis (UC) and Crohn's disease (CD) on the uptake transporters of peptide transporter 1 (PEPT1), which are up-regulated under the inflamed condition. The uptake transport of glycylsarcosine, a typical substrate for PEPT1, was reduced to 60% only by 5-aminosalicylate at the clinically relevant concentration among tested marketed drugs in PEPT1 transfected HEK293 cell lines. These findings suggest that the inhibition of PEPT1, which were up-regulated in inflamed or non-inflamed site on UC and CD patients, contribute to the clinical effect of commercially available drugs for IBD patients through the inhibition of uptake of antigenic proinflammatory oligopeptides such as formyl-methionine (Met)-leucine (Leu)-phenylalanine (Phe) via PEPT1.

Function, Regulation, and Pathophysiological Relevance of the POT Superfamily, Specifically PepT1 in Inflammatory Bowel Disease

Mammalian members of the proton-coupled oligopeptide transporter family are integral membrane proteins that mediate the cellular uptake of di/tripeptides and peptide-like drugs and couple substrate translocation to the movement of H⁺ , with the transmembrane electrochemical proton gradient providing the driving force. Peptide transporters are responsible for the (re)absorption of dietary and/or bacterial di- and tripeptides in the intestine and kidney and maintaining homeostasis of neuropeptides in the brain. These proteins additionally contribute to absorption of a number of pharmacologically important compounds. In this overview article, we have provided updated information on the structure, function, expression, localization, and activities of PepT1 (SLC15A1), PepT2 (SLC15A2), PhT1 (SLC15A4), and PhT2 (SLC15A3). Peptide transporters, in particular, PepT1 are discussed as drug-delivery systems in addition to their implications in health and disease. Particular emphasis has been placed on the involvement of PepT1 in the physiopathology of the gastrointestinal tract, specifically, its role in inflammatory bowel diseases. © 2018 American Physiological Society. Compr Physiol 8:731-760, 2018.

Reduced active transcellular intestinal oxalate secretion contributes to the pathogenesis of obesity-associated hyperoxaluria

Most kidney stones are composed of calcium oxalate, and minor changes in urine oxalate affect the stone risk. Obesity is a risk factor for kidney stones and a positive correlation of unknown etiology between increased body size, and elevated urinary oxalate excretion has been reported. Here, we used obese ob/ob (ob) mice to elucidate the pathogenesis of obesity-associated hyperoxaluria. These ob mice have significant hyperoxaluria (3.3-fold) compared with control mice, which is not due to overeating as shown by pair-feeding studies. Dietary oxalate removal greatly ameliorated this hyperoxaluria, confirming that it is largely enteric in origin. Transporter SLC26A6 (A6) plays an essential role in active transcellular intestinal oxalate secretion, and ob mice have significantly reduced jejunal A6 mRNA (- 80%) and total protein (- 62%) expression. While net oxalate secretion was observed in control jejunal tissues mounted in Ussing chambers, net absorption was seen in ob tissues, due to significantly reduced secretion. We hypothesized that the obesity-associated increase in intestinal and systemic inflammation, as reflected by elevated proinflammatory cytokines, suppresses A6-mediated intestinal oxalate secretion and contributes to obesity-associated hyperoxaluria. Indeed, proinflammatory cytokines (elevated in ob mice) significantly decreased intestinal oxalate transport in vitro by reducing A6 mRNA and total protein expression. Proinflammatory cytokines also significantly reduced active mouse jejunal oxalate secretion, converting oxalate transport from net secretion in vehicle-treated tissues to net absorption in proinflammatory cytokines-treated tissues. Thus, reduced active intestinal oxalate secretion, likely secondary to local and systemic inflammation, contributes to the pathogenesis of obesity-associated hyperoxaluria. Hence, proinflammatory cytokines represent potential therapeutic targets.

Effect of Aging on the Absorption of Small Peptides in Spontaneously Hypertensive Rats

In the present study, we aimed to evaluate the effect of aging on the absorption of small peptides in spontaneously hypertensive rats (SHRs). Three kinds of dipeptides, glycyl-sarcosine (Gly-Sar), Trp-His, and captopril (a dipeptidomimetic drug), a Gly-Sar-Sar tripeptide, a Gly-Sar-Sar-Sar tetrapeptide, and a Gly-Sar-Sar-Sar-Sar pentapeptide were administered at doses of 10 mg/kg each to 8- and 40-week-old SHRs. The peptides were all detected in their intact forms in the blood. There was a significantly promoted absorption of di/tripeptides in aged SHRs compared with young SHRs. In contrast, the absorption of tetra/pentapeptides was not affected by aging. PepT1 expression in the mid-jejunum was significantly increased in 40-week-old SHRs compared with 8-week-old SHRs, whereas aging did not alter the expression of claudin-1, a tight junction related protein. Thus, the present results suggest that SHR aging may enhance the absorption of di/tripeptides through the enhanced PepT1 transport route, although oligopeptides may be absorbed in an age-independent manner.

Dormant cancer cells accumulate high protoporphyrin IX levels and are sensitive to 5-aminolevulinic acid-based photodynamic therapy

Photodynamic therapy (PDT) and diagnosis (PDD) using 5-aminolevulinic acid (ALA) to drive the production of an intracellular photosensitizer, protoporphyrin IX (PpIX), are in common clinical use. However, the tendency to accumulate PpIX is not well understood. Patients with cancer can develop recurrent metastatic disease with latency periods. This pause can be explained by cancer dormancy. Here we created uniformly sized PC-3 prostate cancer spheroids using a 3D culture plate (EZSPHERE). We demonstrated that cancer cells exhibited dormancy in a cell density-dependent manner not only in spheroids but also in 2D culture. Dormant cancer cells accumulated high PpIX levels and were sensitive to ALA-PDT. In dormant cancer cells, transporter expressions of PEPT1, ALA importer, and ABCB6, an intermediate porphyrin transporter, were upregulated and that of ABCG2, a PpIX exporter, was downregulated. PpIX accumulation and ALA-PDT cytotoxicity were enhanced by G0/G1-phase arrestors in non-dormant cancer cells. Our results demonstrate that ALA-PDT would be an effective approach for dormant cancer cells and can be enhanced by combining with a cell-growth inhibitor.

Transportome Profiling Identifies Profound Alterations in Crohn's Disease Partially Restored by Commensal Bacteria

BACKGROUND AND AIMS

Several transport alterations have been described in intestinal inflammatory diseases. This is relevant because the primary function of the intestine is nutrient and mineral absorption. However, analysis of the transportome as a whole and the effect of commensal bacteria on it have not been addressed so far.

METHODS

Five healthy and 6 Crohn's disease (CD) samples were hybridized to human HT-12 V4 Illumina GeneChip. Results were validated by reverse transcription-polymerase chain reaction (RT-PCR) analysis and with additional array data. Organ culture assays were performed from mucosa ileal wall specimens collected at surgery. Samples were incubated with or without commensal bacteria for 4 hours. Finally, RNA was isolated for microarray processing.

RESULTS

The analysis of CD versus healthy ileal mucosa demonstrated upregulation of previously described genes involved in immunity and the inflammatory response in this disease. Interestingly, whole transcriptional analysis revealed profound alterations in the transportome profile. Sixty-two solute carrier (SLC) transporters displayed different expression patterns, most of them being downregulated. Changes were confirmed by RT-PCR in a randomly chosen subset of SLCs. A large number of amino acid transporters and most members of the enteric purinome were found to be altered. Most of these proteins were found at the apical membrane of the enterocyte, which could impair both amino acid absorption and purinergic signalling. Treatment of ileum specimen explants with commensal bacteria restored almost all CD transportome alterations.

CONCLUSIONS

These results describe the altered transportome profile in CD and open the possibility of restoring transportome complications with commensal bacteria.

Intestinal barrier dysfunction: implications for chronic inflammatory conditions of the bowel

The intestinal epithelium of adult humans acts as a differentially permeable barrier that separates the potentially harmful contents of the lumen from the underlying tissues. Any dysfunction of this boundary layer that disturbs the homeostatic equilibrium between the internal and external environments may initiate and sustain a biochemical cascade that results in inflammation of the intestine. Key to such dysfunction are genetic, microbial and other environmental factors that, singularly or in combination, result in chronic inflammation that is symptomatic of inflammatory bowel disease (IBD). The aim of the present review is to assess the scientific evidence to support the hypothesis that defective transepithelial transport mechanisms and the heightened absorption of intact antigenic proinflammatory oligopeptides are important contributing factors in the pathogenesis of IBD.

Salmonella infection inhibits intestinal biotin transport: cellular and molecular mechanisms

Infection with the nontyphoidal Salmonella is a common cause of food-borne disease that leads to acute gastroenteritis/diarrhea. Severe/prolonged cases of Salmonella infection could also impact host nutritional status, but little is known about its effect on intestinal absorption of vitamins, including biotin. We examined the effect of Salmonella enterica serovar Typhimurium (S. typhimurium) infection on intestinal biotin uptake using in vivo (streptomycin-pretreated mice) and in vitro [mouse (YAMC) and human (NCM460) colonic epithelial cells, and human intestinal epithelial Caco-2 cells] models. The results showed that infecting mice with wild-type S. typhimurium, but not with its nonpathogenic isogenic invA spiB mutant, leads to a significant inhibition in jejunal/colonic biotin uptake and in level of expression of the biotin transporter, sodium-dependent multivitamin transporter. In contrast, infecting YAMC, NCM460, and Caco-2 cells with S. typhimurium did not affect biotin uptake. These findings suggest that the effect of S. typhimurium infection is indirect and is likely mediated by proinflammatory cytokines, the levels of which were markedly induced in the intestine of S. typhimurium-infected mice. Consistent with this hypothesis, exposure of NCM460 cells to the proinflammatory cytokines TNF-α and IFN-γ led to a significant inhibition of biotin uptake, sodium-dependent multivitamin transporter expression, and activity of the SLC5A6 promoter. The latter effects appear to be mediated, at least in part, via the NF-κB signaling pathway. These results demonstrate that S. typhimurium infection inhibits intestinal biotin uptake, and that the inhibition is mediated via the action of proinflammatory cytokines.

A high-protein formula increases colonic peptide transporter 1 activity during neonatal life in low-birth-weight piglets and disturbs barrier function later in life

Dietary peptides are absorbed along the intestine through peptide transporter 1 (PepT-1) which is highly responsive to dietary protein level. PepT-1 is also involved in gut homeostasis, both initiating and resolving inflammation. Low-birth-weight (LBW) neonates are routinely fed a high-protein (HP) formula to enhance growth. However, the influence of this nutritional practice on PepT-1 activity is unknown. Intestinal PepT-1 activity was compared in normal-birth-weight (NBW) and LBW piglets. The effect of HP v. normal-protein (NP) formula feeding on PepT-1 activity and gut homeostasis in LBW piglets was evaluated, during the neonatal period and in adulthood. Flux of cephalexin (CFX) across the tissue mounted in Ussing chambers was used as an indicator of PepT-1 activity. CFX flux was greater in the ileum, but not jejunum or colon, of LBW than NBW piglets during the neonatal period. When LBW piglets were formula-fed, the HP formula increased colonic CFX during the 1st week of life. Later in life, intestinal CFX fluxes and barrier function were similar whether LBW pigs had been fed NP or HP formula. However, colonic permeability of HP- but not NP-fed pigs increased when luminal pH was brought to 6·0. The formyl peptide N-formyl methionyl-leucyl-phenylalanine conferred colonic barrier protection in HP-fed piglets. Heat shock protein 27 levels in the colonic mucosa of HP-fed LBW pigs correlated with the magnitude of response to the acidic challenge. In conclusion, feeding a HP formula enhanced colonic PepT-1 activity in LBW pig neonates and increased sensitivity of the colon to luminal stress in adulthood.

Epithelial transport in inflammatory bowel diseases

The epithelium of the gastrointestinal tract is one of the most versatile tissues in the organism, responsible for providing a tight barrier between dietary and bacterial antigens and the mucosal and systemic immune system while maintaining efficient digestive and absorptive processes to ensure adequate nutrient and energy supply. Inflammatory bowel diseases (Crohn's disease and ulcerative colitis) are associated with a breakdown of both functions, which in some cases are clearly interrelated. In this updated literature review, we focus on the effects of intestinal inflammation and the associated immune mediators on selected aspects of the transepithelial transport of macronutrients and micronutrients. The mechanisms responsible for nutritional deficiencies are not always clear and could be related to decreased intake, malabsorption, and excess losses. We summarize the known causes of nutrient deficiencies and the mechanism of inflammatory bowel disease-associated diarrhea. We also overview the consequences of impaired epithelial transport, which infrequently transcend its primary purpose to affect the gut microbial ecology and epithelial integrity. Although some of those regulatory mechanisms are relatively well established, more work needs to be done to determine how inflammatory cytokines can alter the transport process of nutrients across the gastrointestinal and renal epithelia.

Colonic expression of the peptide transporter PEPT1 is downregulated during intestinal inflammation and is not required for NOD2-dependent immune activation

BACKGROUND

PEPT1 was proposed to be expressed only in inflamed colonic tissues in which it could contribute to inflammatory bowel disease (IBD) development by transporting bacterial peptides, such as muramyl dipeptide (MDP), that activate intracellular pattern recognition receptors, such as the nucleotide-binding and oligomerization domain 2. To better define the pathological relevance of this transporter, we analyzed PEPT1 expression during intestinal inflammation and studied the susceptibility of Pept1-deficient (Pept1) mice to experimental colitis.

METHODS

Wild-type and Pept1 mice were treated with dextran sulfate sodium and 2,4,6-trinitrobenzene sulfonic acid to induce colitis, and MDP-induced cytokine expression was studied in colonic tissue cultures. PEPT1 expression was characterized in mouse models of Crohn's disease-like ileitis (Tnf) or colitis (Il-10, Il-10XTlr2) and endoscopic tissue samples from descending colon of patients with IBD (n = 11) and controls (n = 17). Moreover, the prevalence of the PEPT1 single-nucleotide polymorphism rs2297322 was tested in German patients with IBD (n = 458) and controls (n = 452).

RESULTS

PEPT1 expression was consistently reduced under condition of acute or chronic experimental inflammation. Wild-type and Pept1 mice revealed comparable susceptibility to dextran sulfate sodium-induced and 2,4,6-trinitrobenzene sulfonic acid-induced colitis, and MDP-induced cytokine expression was PEPT1-independent. PEPT1 expression levels were also decreased in descending colon of patients with IBD during acute inflammation, but the rs2297322 single-nucleotide polymorphism was not associated with IBD susceptibility in the German cohort.

CONCLUSIONS

PEPT1 expression is reduced during intestinal inflammation and PEPT1 is neither required for MDP-induced immune response nor is the PEPT1 rs2297322 single-nucleotide polymorphism associated with IBD susceptibility in our German cohort. These data strongly argue against a primary role of PEPT1 in the initiation or progression of IBD.

TNFα regulates sugar transporters in the human intestinal epithelial cell line Caco-2

PURPOSE

During intestinal inflammation TNFα levels are increased and as a consequence malabsorption of nutrients may occur. We have previously demonstrated that TNFα inhibits galactose, fructose and leucine intestinal absorption in animal models. In continuation with our work, the purpose of the present study was to investigate in the human intestinal epithelial cell line Caco-2, the effect of TNFα on sugar transport and to identify the intracellular mechanisms involved.

METHODS

Caco-2 cells were grown on culture plates and pre-incubated during different periods with various TNFα concentrations before measuring the apical uptake of galactose, α-methyl-glucoside (MG) or fructose for 15 min. To elucidate the signaling pathway implicated, cells were pre-incubated for 30min with the PKA inhibitor H-89 or the PKC inhibitor chelerythrine, before measuring the sugar uptake. The expression in the apical membrane of the transporters implicated in the sugars uptake process (SGLT1 and GLUT5) was determined by Western blot.

RESULTS

TNFα inhibited 0.1mM MG uptake after pre-incubation of the cells for 6-48h with the cytokine and in the absence of cytokine pre-incubation. In contrast, 5mM fructose uptake was stimulated by TNFα only after long pre-incubation times (24 and 48 h). These effects were mediated by the binding of the cytokine to its specific receptor TNFR1, present in the apical membrane of the Caco-2 cells. Analysis of the expression of the MG and fructose transporters at the brush border membrane of the cells, after 24h pre-incubation with the cytokine, revealed decrease on the amount of SGLT1 and increase on the amount of GLUT5 proteins. Short-term inhibition of MG transport by TNFα was not modified by H-89 but was blocked by chelerythrine.

CONCLUSIONS

SGLT1 and GLUT5 expression in the plasma membrane is regulated by TNFα in the human epithelial cell line Caco-2 cells, leading to alteration on sugars transport, suggesting that TNFα could be considered as a physiological local regulator of nutrients absorption in response to an intestinal inflammatory status.

The peptide transporter PEPT1 is expressed in distal colon in rodents and humans and contributes to water absorption

The peptide transporter PEPT1, expressed in the brush border membrane of enterocytes, mediates the uptake of di- and tripeptides from luminal protein digestion in the small intestine. PEPT1 was proposed not to be expressed in normal colonic mucosa but may become detectable in inflammatory states such as Crohn's disease or ulcerative colitis. We reassessed colonic expression of PEPT1 by performing a systematic analysis of PEPT1 mRNA and protein levels in healthy colonic tissues in mice, rats, and humans. Immunofluorescence analysis of different mouse strains (C57BL/6N, 129/Sv, BALB/c) demonstrated the presence of PEPT1 in the distal part of the colon but not in proximal colon. Rat and human intestines display a similar distribution of PEPT1 as found in mice. However, localization in human sigmoid colon revealed immunoreactivity present at low levels in apical membranes but substantial staining in distinct intracellular compartments. Functional activity of PEPT1 in colonic tissues from mice was assessed in everted sac preparations using [¹⁴C]Gly-Sar and found to be 5.7-fold higher in distal compared with proximal colon. In intestinal tissues from Pept1-/- mice, no [¹⁴C]Gly-Sar transport was detectable but feces samples revealed significantly higher water content than in wild-type mice, suggesting that PEPT1 contributes to colonic water absorption. In conclusion, our studies unequivocally demonstrate the presence of PEPT1 protein in healthy distal colonic epithelium in mice, rats, and humans and proved that the protein is functional and contributes to electrolyte and water handling in mice.

Expression of proton-coupled oligopeptide transporter (POTs) in prostate of mice and patients with benign prostatic hyperplasia (BPH) and prostate cancer (PCa)

BACKGROUND

Proton-coupled oligopeptide transporters (POTs) serve as integral membrane protein for the cellular uptake of di/tripeptide. Prostate has a large requirement of nutriment for its function to produce and secrete prostatic fluid. Besides, prostate suffered from limited therapy effect of drug treatment. Thus present study was performed to evaluate the expression of POTs in prostate of mice and human with the aim to provide information for potential role of POTs in absorption of nutriment and peptidomimetic drugs in prostate.

METHODS

Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot methods were applied to study the mRNA, protein expression of POTs in prostate, human prostate cancer cells (PC-3), and human prostate epithelial cells (RWPE-1).

RESULTS

qRT-PCR study showed different characteristic of POTs mRNA expression in mouse prostate. Among these transporters, protein expression of PepT2 was detected and increasing during the development of mouse prostate, while PepT1, PHT1, and PHT2 protein was not detected. Furthermore, different characteristic of regulation by inflammation on POTs mRNA expression was found in RWPE-1 and PC-3. In addition, mRNA expression of PepT2 and PHT1 in prostate of patients with PCa was demonstrated be lower compared with BPH.

CONCLUSIONS

These findings provide the first evidence for the expression of POTs in prostate of mice and patients with BPH or PCa and suggest that POTs are likely to play a role in the transport of di/tripeptides and peptidomimetics in prostate.

Ontogeny of dipeptide uptake and peptide transporter 1 (PepT1) expression along the gastrointestinal tract in the neonatal Yucatan miniature pig

The H+-coupled transporter, peptide transporter 1 (PepT1), is responsible for the uptake of dietary di- and tripeptides in the intestine. Using an in vivo continuously perfused gut loop model in Yucatan miniature pigs, we measured dipeptide disappearance from four 10 cm segments placed at equidistant sites along the length of the small intestine. Pigs were studied at 1, 2, 3 (suckling) and 6 weeks (post-weaning) postnatal age. Transport capability across the PepT1 transporter was assessed by measuring the disappearance of 3H-glycylsarcosine; real-time RT-PCR was also used to quantify PepT1 mRNA. Each of the regions of intestine studied demonstrated the capacity for dipeptide transport. There were no differences among age groups in transport rates measured in the most proximal intestine segment. Transport of 3H-glycylsarcosine was significantly higher in the ileal section in the youngest age group (1 week) compared with the other the suckling groups; however, all suckling piglet groups demonstrated lower ileal transport compared with the post-weaned pigs. Colonic PepT1 mRNA was maximal in the earliest weeks of development and decreased to its lowest point by week 6. These results suggest that peptide transport in the small intestine may be of importance during the first week of suckling and again with diet transition following weaning.

The role and pathophysiological relevance of membrane transporter PepT1 in intestinal inflammation and inflammatory bowel disease

Intestinal inflammation is characterized by epithelial disruption, leading to loss of barrier function and the recruitment of immune cells, including neutrophils. Although the mechanisms are not yet completely understood, interactions between environmental and immunological factors are thought to be critical in the initiation and progression of intestinal inflammation. In recent years, it has become apparent that the di/tripeptide transporter PepT1 may play an important role in the pathogenesis of such inflammation. In healthy individuals, PepT1 is primarily expressed in the small intestine and transports di/tripeptides for metabolic purposes. However, during chronic inflammation such as that associated with inflammatory bowel disease, PepT1 expression is upregulated in the colon, wherein the protein is normally expressed either minimally or not at all. Several recent studies have shown that PepT1 binds to and transports various bacterial di/tripeptides into colon cells, leading to activation of downstream proinflammatory responses via peptide interactions with innate immune receptors. In the present review, we examine the relationship between colonic PepT1-mediated peptide transport in the colon and activation of innate immune responses during disease. It is important to understand the mechanisms of PepT1 action during chronic intestinal inflammation to develop future therapies addressing inappropriate immune activation in the colon.

Cytokine regulation of OCTN2 expression and activity in small and large intestine

BACKGROUND

The organic cation transporter OCTN2 is located on the IBD5 risk allele and has been implicated in the pathogenesis of inflammatory bowel diseases (IBD). OCTN2 is expressed in the apical membrane and transports many solutes including bacteria-derived mediators that may be involved in host-microbial interactions. To explore its role further, we examined potential regulatory factors in human IBD and in experimental models of OCTN2 expression.

METHODS

Human colonic epithelial cells (Caco2BBE) were used to investigate the effects of inflammatory mediators on OCTN2 activity and expression. Apical membrane expression of OCTN2 was assessed by surface biotinylation. Rag-1(-/-) -deficient mice were used to determine the potential role of adaptive immune cells in the regulation of OCTN2 expression. C57Bl/6 mice were treated with the cytokines interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α) to determine the effects on OCTN2 expression and activity. OCTN2 expression in human IBD specimens was assessed by Western blotting and immunohistochemistry.

RESULTS

OCTN2 activity and expression are regulated by the state of intestinal inflammation. OCTN2 expression in colonic tissues of Rag-1(-/-) -deficient mice was reduced. Treatment with IFN-γ and TNF-α increased intestinal OCTN2 expression, particularly in the colon. IFN-γ increased both total and apical membrane expression of Caco2BBE OCTN2, whereas TNF-α stimulated apical expression. Colonic epithelial OCTN2 expression was increased in actively inflamed areas of both Crohn's disease and ulcerative colitis.

CONCLUSIONS

Intestinal epithelial OCTN2 expression is increased by intestinal inflammation, most likely through increased levels of proinflammatory cytokines. These findings suggest that OCTN2 may participate to restoration of intestinal homeostasis under conditions of inflammation-associated stress.

Lactobacillus plantarum consumption increases PepT1-mediated amino acid absorption by enhancing protein kinase C activity in spontaneously colitic mice

Although probiotic consumption has generally been shown to have many beneficial effects for the prevention and treatment of inflammatory bowel disease, the effects of Lactobacillus plantarum (LP) on intestinal nutrient absorption, particularly oligopeptide transporter 1 (PepT1)-mediated absorption of dietary protein under inflammatory conditions, has not yet been characterized. In this study, we first investigated the effects of LP consumption on plasma amino acid concentrations and PepT1-mediated absorption of cephalexin in the small intestine of wild-type (WT) mice and interleukin-10 knockout (IL-10(-/-)) mice, a model of spontaneous colitis. We then analyzed expression and distribution of PepT1 and protein kinase C (PKC) activity in the jejunum of these mice. LP consumption (10(9) colony-forming units/0.5 mL) delivered by gavage once per day for 4 wk increased the total plasma amino acid concentration and the concentration of plasma cephalexin through enhancement of PepT1-mediated uptake in LP treated IL-10(-/-) mice compared with IL-10(-/-) mice. However, Western blotting and quantitative PCR analysis revealed no significant differences in PepT1 protein and mRNA expression between LP-treated and untreated mice. Additionally, immunofluorescence analysis showed that PepT1 did not appear to be mislocalized in IL-10(-/-) mice. Interestingly, IL-10(-/-) mice had significantly lower PKC activity and expression of phosphorylated PKC compared with WT mice, and these decreases could be prevented by LP treatment. These data suggest that consumption of LP enhances PepT1-mediated amino acid absorption, likely through alterations in PKC activity, as opposed to changes in expression or distribution of PepT1 in the small intestine of IL-10(-/-) mice.

PepT1 oligopeptide transporter (SLC15A1) gene polymorphism in inflammatory bowel disease

BACKGROUND

Human polymorphisms affecting gut epithelial barrier and interactions with bacteria predispose to the inflammatory bowel diseases (IBD) Crohn's disease (CD) and ulcerative colitis (UC). The intestinal transporter PepT1, encoded by the SLC15A1 gene, mediates intracellular uptake of bacterial products that can induce inflammation and NF-kappaB activation upon binding to NOD2, a protein often mutated in CD. Hence, we tested SLC15A1 polymorphisms for association with IBD.

METHODS

Twelve SLC15A1 single nucleotide polymorphisms (SNPs) were genotyped in 1783 individuals from 2 cohorts of Swedish and Finnish IBD patients and controls. An in vitro system was set up to evaluate the potential impact of SLC15A1 polymorphism on PepT1 transporter function by quantification of NOD2-mediated activation of NF-kappaB.

RESULTS

The common allele (C) of a coding polymorphism (rs2297322, Ser117Asn) was associated with CD susceptibility both in Sweden and in Finland, but with genetic effects in opposite directions (risk and protection, respectively). The best evidence of association was found in both populations when the analysis was performed on individuals not carrying NOD2 common risk alleles (Sweden allelic P = 0.0007, OR 1.97, 95% confidence interval [CI] 1.34-2.92; Finland genotype P = 0.0013, OR 0.63, 95% CI 0.44-0.90). The PepT1 variant encoded by the C allele (PepT1-Ser117) was associated with reduced signaling downstream of NOD2 (P < 0.0001 compared to Pept1-Asn117).

CONCLUSIONS

A functional polymorphism in the SLC15A1 gene might be of relevance to inflammation and antibacterial responses in IBD. Whether this polymorphism truly contributes to disease susceptibility needs to be further addressed, and should stimulate additional studies in other populations.

Changes in mRNA expression levels of solute carrier transporters in inflammatory bowel disease patients

Inflammatory bowel disease (IBD) is an inflammatory condition that affects the gastrointestinal tract. The solute carrier (SLC) superfamily of transporters comprise proteins involved in the uptake of drugs, hormones, and other biologically active compounds. The purpose of this study was to determine the mRNA expression levels of 15 solute carrier transporters in two regions of the intestine in IBD patients. Endoscopic biopsy specimens were taken from two locations (terminal ileum and colon) for histological examination and RNA extraction. We quantitatively measured the mRNA expression of 15 SLC transporters in 107 IBD patients (53 with Crohn's disease and 54 with ulcerative colitis) and 23 control subjects. mRNA expression was evaluated using the quantitative reverse transcription-polymerase chain reaction technique. We observed that in the ileum of IBD patients, mRNA levels for serotonin transporter, equilibrative nucleoside transporter (ENT) 1, ENT2, and organic anion-transporting polypeptide (OATP) 2B1 were significantly elevated, whereas levels for apical sodium-dependent bile acid transporter (ASBT) and organic zwitterion/cation transporter (OCTN) 2 were significantly lower. In colon, mRNA levels for ENT1, ENT2, concentrative nucleoside transporter (CNT) 2, OATP2B1, and OATP4A1 were significantly higher, whereas mRNA levels for OCTN2 were significantly decreased. In inflamed colon of IBD patients the mRNA expression levels of ENT1, ENT2, CNT2, OATP2B1, OATP4A1, and peptide transporter 1 were significantly higher. We conclude that intestinal SLC mRNA levels are dysregulated in IBD patients, which may be linked to the inflammation of the tissue and provides an indication about the role of inflammatory signaling in regulation of SLC expression.

Evidence for intestinal heterogenic expression of di-tripeptides transporter PepT1 during experimental cryptosporidiosis in neonatal rats

Cryptosporidium parvum is a protozoan parasite that causes intestinal malabsorptive syndrome and malnutrition. Considering the importance of di-tripeptide absorption for nutritional status, we previously investigated the regulation of PepT1 transporter in the suckling rat model of acute cryptosporidiosis and showed that PepT1 protein expression and activity were not modified in the parasitized intestine. Here we used confocal microscopy performed on intestinal villi to determine the subcellular localization of PepT1 together with f-actin and parasites. For this purpose, confocal microscopy using vibratome thick sections was developed on the distal small intestine, the preferential site of parasite implantation. Results showed major heterogeneity of apical PepT1 expression among enterocytes, which did not correlate with actin staining or parasite implantation. These results underscore the importance of considering the effect of C. parvum at the cellular scale and not only in the entire epithelium.

Peptide transporters and their roles in physiological processes and drug disposition

1. The peptide transporters belong to the peptide transporter (PTR) family and serve as integral membrane proteins for the cellular uptake of di- and tripeptides in the organism. By their ability also to transport peptidomimetics and other substrates with therapeutic activities or precursors of pharmacologically active agents, they are of considerable importance in pharmacology. 2. PEPT1 is the low-affinity, high-capacity transporter and is mainly expressed in the small intestine, whereas PEPT2 is the high-affinity, low-capacity transporter and has a broader distribution in the organism. 3. Targeted mouse models have revealed PEPT2 to be the dominant transporter for the reabsorption of di- and tripeptides and its pharmacological substrates in the organism, and for the removal of these substrates from the cerebrospinal fluid. Moreover, the peptide transporters undergo physiological and pharmacological regulation and, of great interest, are present in disease states where PEPT1 exhibits ectopic expression in colonic inflammation. 4. The paper reviews the structural characteristics of the peptide transporters, the structural requirements for substrates, the distribution of the peptide transporters in the organism, and finally their regulation in the organism in healthy and pathological situations.

Malnutrition as an enteric infectious disease with long-term effects on child development

Malnutrition is a major contributor to mortality and is increasingly recognized as a cause of potentially lifelong functional disability. Yet, a rate-limiting step in achieving normal nutrition may be impaired absorptive function due to multiple repeated enteric infections. This is especially problematic in children whose diets are marginal. In malnourished individuals, the infections are even more devastating. This review documents the evidence that intestinal infections lead to malnutrition and that malnutrition worsens intestinal infections. The clinical data presented here derive largely from long-term cohort studies that are supported by controlled animal studies. Also reviewed are the mechanisms by which enteric infections lead to undernutrition and by which malnutrition worsens enteric infections, with implications for potential novel interventions. Further intervention studies are needed to document the relevance of these mechanisms and, most importantly, to interrupt the vicious diarrhea-malnutrition cycle so children may develop their full potential.

Changtai granule, a traditional Chinese drug, protects hapten-induced colitis by attenuating inflammatory and immune dysfunctions

The study was aimed to investigate the effects and mechanism of action of Changtai granule (CT), a traditional compound Chinese medicinal formula, in rodent 2,4,6-trinitrobenzene sulfonic acid (TNBS) colitis. Rats with TNBS/ethanol-induced colitis were used. The colonic wet weight, myeloperoxidase (MPO) activity, macroscopic and histological colon injury was observed. Inflammation cytokines were determined by ELISA methods and semi-quantitative RT-PCR. When dosed orally once daily, CT markedly attenuated TNBS-induced colitis. CT significantly attenuated colonic wet weight, macroscopic and histological colon injury. CT decreased mucosal mRNA levels for several inflammatory mediators: inducible nitric oxide synthase, cyclooxygenase 2, and macrophage inflammatory protein 2. CT also decreased mucosal mRNA and protein levels of T effectors cytokines: tumor necrosis factor-alpha (TNF-alpha), interleukin-2 (IL-2) and interferon-gamma (IFN-gamma). Systemic levels of these cytokines were also dramatically attenuated. CD3/CD28-mediated costimulation of T helper 1 effector cytokines release in lamina propria mononuclear cells (LPMC) was markedly inhibited by CT ex vivo and in vitro. Also CT prevented cytokines production by nuclear factor-kappaB (NF-kappaB). The potential anti-inflammatory and immunomodulatory effect of CT in TNBS colitis suggests that CT may be an effective treatment approach for inflammatory bowel disease.

Molecular cloning and promoter analysis of downregulated in adenoma (DRA)

Downregulated in adenoma (DRA), also referred to as SLC26A3, is an intestinal anion transporter essential for intestinal chloride absorption. Mutations in DRA result in congenital chloride diarrhea. DRA expression has been shown to be induced by differentiation and to be modulated by cytokines. However, mechanisms of DRA gene transcription and its tissue-specific targeting have not yet been investigated. In this study, we cloned a 3,765-bp promoter fragment of human DRA gene and characterized its activity in human colonic LS174T and Caco-2 human colon cell lines. Primer extension identified a single transcriptional initiation site that was identical in both colon cancer cell lines and normal colon. Although hepatic nuclear factor HNF-4 is involved in the basal activity of DRA promoter, sodium butyrate induces its activity in LS174T cells via the binding of Yin Yang 1 (YY1) and GATA transcription factors to their respective cis-elements in promoter region. We also demonstrated a reduction in DRA promoter activity in Caco-2 cells by IFN-gamma, suggesting that regulation of DRA promoter by IFN-gamma may contribute to the pathophysiology of intestinal inflammation. Furthermore, we showed that the DRA promoter fragment is sufficient to drive human growth hormone transgene expression specifically in villus epithelial cells of the small intestine and in differentiated upper crypt and surface epithelial cells of the colon. Our studies provide evidence for the involvement of HNF-4, YY1, and GATA transcription factors in DRA expression in intestinal differentiated epithelial cells.

Regulation of the oligopeptide transporter, PEPT-1, in DSS-induced rat colitis

The effect of colitis induced with dextran sodium sulfate (DSS) in rats on the bioavailability of drugs transported by the oligopeptide transporter PepT-1 was analyzed by studying the pharmacokinetics of PepT-1 substrates: cephalexin and valacyclovir, the prodrug of antiviral acyclovir. Western blot, immunohistochemistry, and real-time PCR were used to determine the PepT-1 protein and gene expression. We observed (1) no significant modification of PepT-1 expression in the duodenum and jejunum; (2) a slight decrease in both PepT-1 mRNA (50%) and protein expression (25%) in the ileum following DSS challenge; and (3) ectopic PepT-1 immunostaining in regenerative hyperplasia segments in the distal colon from DSS-treated rats where focal inflammation is localized. However, no modification of pharmacokinetic parameters (C (max), T (max), AUC) of cephalexin or acyclovir was detected. In conclusion, DSS-induced rat colitis did not alter PepT-1 substrate bioavailability despite certain modifications in PepT-1 expression profile.

Gene expression and regulation of drug transporters in the intestine and kidney

Intestinal absorption and renal secretion of ionic drugs are controlled by a number of drug transporters expressed at the brush-border and basolateral membranes of epithelial cells. Over the last several years, considerable progress has been made regarding the molecular identification and functional characterization of drug transporters. Under some physiological and pathophysiological conditions, the expression and transport activity of drug transporters are changed, affecting the pharmacokinetics of substrate drugs. The regulation of transport activity in response to endogenous and exogenous signals can occur at various levels such as transcription, mRNA stability, translation, and posttranslational modification. Transcriptional regulation is of particular interest, because changes in transport activity are dynamically regulated by increases or decreases in levels of mRNA expression. The tissue-specific expression of drug transporters is also under transcriptional control, and recent studies using clinical samples from human tissues have revealed the expression profiles of drug transporters in the human body. The purpose of this research updates is to review the recent progress in the study of the gene expression and regulation of intestinal and renal drug transporters.