Abnormal expression of the peptide transporter PepT1 in the colon of massive bowel resection rat: a potential route for colonic mucosa damage by transport of fMLP

Enteral feeding strategies in patients with acute gastrointestinal injury: From limited to progressive to open feeding

Acute gastrointestinal injury (AGI) is very common in critically ill patients, and its severity is positively correlated with mortality. Critically ill patients with digestive and absorption dysfunction caused by AGI face higher nutritional risks, making nutritional support particularly important. Early enteral nutrition (EN) support is extremely important because it can promote the recovery of intestinal function, protect the intestinal mucosal barrier, reduce microbiota translocation, reduce postoperative complications, shorten hospital stay, and improve clinical prognosis. In recent years, many nutritional guidelines have been proposed for critically ill patients; however, there are few recommendations for the implementation of EN in patients with AGI, and their quality of evidence is low. The use of EN feeding strategies in critically ill patients with AGI remains controversial. The aim of this review was to elaborate on how EN feeding strategies should transition from limited to progressive to open feeding and explain the time window for this transition.

Small peptide formulas versus standard polymeric formulas in critically ill patients with acute gastrointestinal injury: a systematic review and meta-analysis

Small peptide formulas versus standard polymeric formulas for enteral nutrition in critically ill patients with acute gastrointestinal injury (AGI) have been a topic of debate. A systematic review and meta-analysis were conducted to compare their clinical and nutritional outcomes. Relevant studies from January 1980 to June 2022 were searched in PubMed, Cochrane, and Embase databases. Randomized controlled trials involving AGI grade I-IV patients were included, while children, non-AGI patients, and non-critically ill patients were excluded. Results indicated no significant difference in all-cause mortality. Patients receiving small peptide formulas showed higher daily protein intake, greater albumin growth, and higher prealbumin levels. They also had shorter lengths of stay in the intensive care unit and hospital. Conversely, patients receiving standard polymeric formulas had a higher daily calorie intake. In conclusion, the choice of formula may not affect mortality in critically ill patients with AGI. Small peptide formulas were more conducive to increase daily protein intake, decrease intensive care unit and hospital length of stay. Further large-scale randomized controlled trials evaluating the effects of these two nutritional formulas on clinical and nutritional outcomes in critically ill patients with AGI are needed to confirm these results.

Serum of limb remote ischemic postconditioning inhibits fMLP-triggered activation and reactive oxygen species releasing of rat neutrophils

Objectives

The study explores the protective role of the peripheral serum of limb remote ischemic postconditioning (LRIP) in reducing the reactive oxygen species (ROS) levels and neutrophil activation, which are responsible for the deleterious reperfusion injury.

Methods

LRIP was induced in Sprague–Dawley rats by three cycles of 5 min occlusion /5 min reperfusion on the left hind limb. The blood samples were collected before LRIP or 0 and 1 h after LRIP (named Serum_Sham, Serum_LRIP0, Serum_LRIP1, respectively). The effects of LRIP serum on ROS level and neutrophils activation were determined. The expression of MyD88-TRAF6-MAPKs and PI3K/AKT pathways in neutrophils were examined.

Results

When compared with Serum_Sham, Serum_LRIP0 and Serum_LRIP1 significantly reduced the ROS released from neutrophils activated by fMLP. Meanwhile, the mRNA expression levels of NADPH oxidase subunit p22^phox and multiple ROS-producing related key proteins, such as NADPH oxidase subunit p47^phox ser 304, ser 345. MyD88, p-ERK, p-JNK and p-P38 expression of neutrophils were downregulated by Serum_LRIP0 and Serum_LRIP1. Serum_LRIP1 also downregulated p47^phox mRNA expression and tumor necrosis factor receptor-associated factor 6 (TRAF6) protein expression.

Conclusion

LRIP serum protects against ROS level and neutrophils activation involving the MyD88-TRAF6-MAPKs. This finding provides new insight into the understanding of LRIP mechanisms.

Cysteinyl-glycine reduces mucosal proinflammatory cytokine response to fMLP in a parenterally-fed piglet model

BACKGROUND

PepT1 transports dietary and bacterial peptides in the gut. We hypothesized that cysteinyl-glycine would ameliorate the inflammatory effect of a bacterial peptide, formyl-methionyl-leucyl-phenylalanine (fMLP), in both sow-fed and parenterally-fed piglets.

METHODS

An intestinal perfusion experiment was performed in piglets (N = 12) that were sow-reared or provided with parenteral nutrition (PN) for 4 d. In each piglet, five segments of isolated intestine were perfused with five treatments including cysteine and glycine, cysteinyl-glycine, fMLP, free cysteine and glycine with fMLP, or cysteinyl-glycine with fMLP. Mucosal cytokine responses and intestinal morphology was assessed in each gut segment.

RESULTS

PN piglets had lower mucosal IL-10 by approximately 20% (P < 0.01). Cysteinyl-glycine lowered TNF-α response to fMLP in PN-fed animals and IFN-γ response to fMLP in both groups (P < 0.05). The free cysteine and glycine treatment reduced TNF-α in sow-fed animals (P < 0.05). fMLP affected villus height in parenterally (P < 0.05), but not sow-fed animals.

CONCLUSION

Parenteral feeding conferred a susceptibility to mucosal damage by fMLP. The dipeptide was more effective at attenuating the inflammatory response to a bacterial peptide than free amino acids. This may be due to competitive inhibition of fMLP transport or a greater efficiency of transport of dipeptides.

Critical role of PepT1 in promoting colitis-associated cancer and therapeutic benefits of the anti-inflammatory PepT1-mediated tripeptide KPV in a murine model

BACKGROUND AND AIMS

The human intestinal peptide transporter 1, hPepT1, is expressed in the small intestine at low levels in the healthy colon and upregulated during inflammatory bowel disease. hPepT1 plays a role in mouse colitis and human studies have demonstrated that chronic intestinal inflammation leads to colorectal cancer (colitis-associated cancer; CAC). Hence, we assessed here the role of PepT1 in CAC.

METHODS

Mice with hPepT1 overexpression in intestinal epithelial cells (TG) or PepT1 (PepT1-KO) deletion were used and CAC was induced by AOM/DSS.

RESULTS

TG mice had larger tumor sizes, increased tumor burdens, and increased intestinal inflammation compared to WT mice. Conversely, tumor number and size and intestinal inflammation were significantly decreased in PepT1-KO mice. Proliferating crypt cells were increased in TG mice and decreased in PepT1-KO mice. Analysis of human colonic biopsies revealed an increased expression of PepT1 in patients with colorectal cancer, suggesting that PepT1 might be targeted for the treatment of CAC. The use of an anti-inflammatory tripeptide KPV (Lys-Pro-Val) transported by PepT1 was able to prevent carcinogenesis in WT mice. When administered to PepT1-KO mice, KPV did not trigger any of the inhibitory effect on tumorigenesis observed in WT mice.

CONCLUSIONS

The observations that pepT1 was highly expressed in human colorectal tumor and that its overexpression and deletion in mice increased and decreased colitis associated tumorigenesis, respectively, suggest that PepT1 is a potential therapeutic target for the treatment of colitis associated tumorigenesis.

Nod2-Rip2 Signaling Contributes to Intestinal Injury Induced by Muramyl Dipeptide Via Oligopeptide Transporter in Rats

BACKGROUND AND AIMS

PepT1 can transport bacterial oligopeptide products and induce intestinal inflammation. Our aim was to investigate the mechanism of the small intestine injury induced by bacterial oligopeptide product muramyl dipeptide (MDP) which is transported by PepT1.

METHODS

We perfused the jejunum with a solution with or without MDP, or with a solution of MDP + Gly-Gly and explored the degree of inflammation to determine the role of PepT1-Nod2 signaling pathway in small intestine mucosa.

RESULTS

MDP perfusion induced inflammatory cell accumulation and intestinal damage, accompanied by an increase in mucosal Nod2 and Rip2 transcript expression. NFκB activity and inflammatory cytokine expression, including serum levels of TNF-α, IL-1β, and IL-6, increased in the MDP group compared to the controls; these effects were reversed by perfusion of the nutritional dipeptide Gly-Gly.

CONCLUSION

MDP can be transported through PepT1, causing inflammatory damage in the rat small intestine. Nod2-Rip2-NFκB signaling involved in the small intestinal inflammatory injury caused by MDP which is transported through PepT1.

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.

Morphological adaptation with preserved proliferation/transporter content in the colon of patients with short bowel syndrome

In short bowel syndrome (SBS), although a remaining colon improves patient outcome, there is no direct evidence of a mucosal colonic adaptation in humans. This prospective study evaluates morphology, proliferation status, and transporter expression level in the epithelium of the remaining colon of adult patients compared with controls. The targeted transporters were Na+/H+ exchangers (NHE2 and 3) and oligopeptide transporter (PepT1). Twelve adult patients with a jejuno-colonic anastomosis were studied at least 2 yr after the last surgery and compared with 11 healthy controls. The depth of crypts and number of epithelial cells per crypt were quantified. The proliferating and apoptotic cell contents were evaluated by revealing Ki67, PCNA, and caspase-3. NHE2, NHE3, PepT1 mRNAs, and PepT1 protein were quantified by quantitative RT-PCR and Western blot, respectively. In patients with SBS compared with controls, 1) hyperphagia and severe malabsorption were documented, 2) crypt depth and number of cells per crypt were 35% and 22% higher, respectively (P < 0.005), whereas the proliferation and apoptotic levels per crypt were unchanged, and 3) NHE2 mRNA was unmodified; NHE3 mRNA was downregulated near the anastomosis and unmodified distally, and PepT1 mRNA and protein were unmodified. We concluded that, in hyperphagic patients with SBS with severe malabsorption, adaptive colonic changes include an increased absorptive surface with an unchanged proliferative/apoptotic ratio and well-preserved absorptive NHE2, NHE3, and PepT1 transporters. This is the first study showing a controlled nonpharmacological hyperplasia in the colon of patients with SBS.

Short Bowel Syndrome

Short bowel syndrome (SBS) is a relatively common, often lethal, and highly costly medical problem in North America. Necrotizing enterocolitis (NEC) is the leading cause of SBS in the United States. An important fact to remember is that the length of the small bowel in a 28-week preterm infant is about 150 cm and in a term infant is about 250 cm. Twenty percent of this length is generally sufficient to allow dependence on parenteral nutrition (PN) via intestinal adaptation. This process is driven by significant increases in circulating trophic hormones, such as cholecystokinin, epidermal and keratinocyte growth factors, growth hormone, insulin-like growth factor-1, and glucagon-like peptide-2. These hormones produce hypertrophy and hyperplasia of the villi, along with increases in specific brush border membrane absorption mechanisms, such as glucose-sodium cotransport (via SGLT-1) and peptide transport (via Pep-T1). Currently, the best clinical markers of intestinal adaptation are the calculated percentage of enteral versus parenteral calories in a growing infant who has SBS and the serum concentrations of citrulline, an amino acid synthesized by mature enterocytes that has been used as a measure of functional intestinal mass.

Butyrate transcriptionally enhances peptide transporter PepT1 expression and activity

Background

PepT1, an intestinal epithelial apical di/tripeptide transporter, is normally expressed in the small intestine and induced in colon during chronic inflammation. This study aimed at investigating PepT1 regulation by butyrate, a short-chain fatty acid produced by commensal bacteria and accumulated inside inflamed colonocyte.

Results

We found that butyrate treatment of human intestinal epithelial Caco2-BBE cells increased human PepT1 (hPepT1) promoter activity in a dose- and time-dependent manner, with maximal activity observed in cells treated with 5 mM butyrate for 24 h. Under this condition, hPepT1 promoter activity, mRNA and protein expression levels were increased as assessed by luciferase assay, real-time RT-PCR and Western blot, respectively. hPepT1 transport activity was accordingly increased by ∼2.5-fold. Butyrate did not alter hPepT1 mRNA half-life indicating that butyrate acts at the transcriptional level. Molecular analyses revealed that Cdx2 is the most important transcription factor for butyrate-induced increase of hPepT1 expression and activity in Caco2-BBE cells. Butyrate-activated Cdx2 binding to hPepT1 promoter was confirmed by gel shift and chromatin immunoprecipitation. Moreover, Caco2-BBE cells overexpressing Cdx2 exhibited greater hPepT1 expression level than wild-type cells. Finally, treatment of mice with 5 mM butyrate added to drinking water for 24 h increased colonic PepT1 mRNA and protein expression levels, as well as enhanced PepT1 transport activity in colonic apical membranes vesicles.

Conclusions

Collectively, our results demonstrate that butyrate increases PepT1 expression and activity in colonic epithelial cells, which provides a new understanding of PepT1 regulation during chronic inflammation.