Changes of biological functions of dipeptide transporter (PepT1) and hormonal regulation in severe scald rats

An update on the effects of food-derived active peptides on the intestinal microecology

The intestinal microecology is a research hotspot, and neologisms related to the gut such as gut-brain axis, gut-lung axis, gut-bone axis, gut-skin axis, gut-renal axis, and gut-liver axis have emerged from recent research. Meticulous investigation has discovered that food-derived active peptides (FDAPs) are bioactive substances that optimize the structure of the gut microbiota to improve human health. However, few reviews have summarized and emphasized the nutritional value of FDAPs and their mechanisms of action in regulating the composition of the gut microbiota. We aim to provide an update on the latest research on FDAPs by comparing, summarizing, and discussing the potential food sources of FDAPs, their physiological functions, and regulatory effects on the intestinal microecology. The key findings are that few studies have analyzed the potential mechanisms and molecular pathways through which FDAPs maintain intestinal microecological homeostasis. We found that an imbalance in the ratio of Bacteroidetes and Firmicutes in the gut microbiota and abnormal production of short-chain fatty acids are key to the occurrence and development of various diseases. This review provides theoretical support for future comprehensive research on the digestion, distribution, metabolism, and excretion of FDAPs and the mechanisms underlying the interactions between FDAPs and the intestinal microecology.

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.

Ethanol inhibits functional activity of the human intestinal dipeptide transporter hPepT1 expressed in Xenopus oocytes

BACKGROUND

The pathological effects of high alcohol (ethanol) consumption on gastrointestinal and hepatic systems are well recognized. However, the effects of ethanol intake on gastric and intestinal absorption and transport systems remain unclear. The present study investigates the effects of ethanol on the human peptide transporter 1 (hPepT1) which mediates the transport of di-and tripeptides as well as several orally administered peptidomimetic drugs such as beta-lactam antibiotics (e.g., penicillin), angiotensin-converting enzyme inhibitors, the anti-neoplastic agent bestatin, and prodrugs of acyclovir.

METHODS

Xenopus oocytes were injected with hPepT1 cRNA and incubated for 3 to 10 days. Currents induced by glycyl-sarcosine (Gly-Sar), Ala-Ala (dipeptides), penicillin and enalapril measured in the presence or absence of ethanol were determined using an 8-channel 2-electrode voltage clamp system, with a membrane potential of -70 mV and 11 voltage steps of 100 milliseconds (from +50 mV to -150 mV in -20 mV increments).

RESULTS

Ethanol (200 mM) inhibited Gly-Sar and Ala-Ala currents by 42 and 30%, respectively, with IC(50)s of 184 and 371 mM, respectively. Ethanol reduced maximal transport capacity (I(max)) of hPepT1 for Gly-Sar without affecting Gly-Sar binding affinity (K(0.5) and Hill coefficient). Penicillin- and enalapril-induced currents were significantly less than those induced by dipeptides and were not inhibited by ethanol.

CONCLUSION

Ethanol significantly reduced transport of dipeptides via a reduction in transport capacity, rather than competing for binding sites in hPepT1. Ethanol inhibition or alteration of transport function may be a primary causative factor contributing to both the nutritional deficits as well as the immunological deficiencies that many alcoholics experience including alcohol liver disease and brain damage.

Apoptosis and functional changes of dipeptide transporter (PepT1) in the rat small intestine after traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) can induce significant alterations of intestinal mucosal structure and barrier function. However, it has not been investigated whether, and to what degree, apoptosis and alterations of absorptive function in the intestinal mucosal epithelium occur after TBI.

MATERIAL AND METHODS

Male Wistar rats were randomly divided into seven groups (five rats each group) including normal group, control group with sham operation, and TBI groups at hours 3, 12, 24, and 72, and on day 7. Parietal brain contusion was adopted using weight-dropping method. Intestinal mucosal structure was examined using histomorphmetric study and electron microscopy, and apoptosis was detected by TUNEL method. An everted sleeve of intestine was securely incubated in Kreb's solution with radioactive dipeptide ((3)H-Gly-Sar, 10 microCi/mL) to measure the uptake and transport of PepT1 of small intestinal epithelial cells.

RESULTS

The villous height, crypt depth and surface area were significantly decreased at 24 h after TBI, and further declined to the degree of mucosal atrophy on day 7 after TBI. Apoptotic changes of condensed nuclei in epithelial cells and fractured, distorted, and sparse microvilli were found by electron microscopy. The number of apoptotic cells in the mucosal epithelium was significantly increased since 3 h after TBI, peaked at 72 h post-injury, then declined at 7 days, but was still higher than that of control. There was a highly negative relation between the apoptotic index and the villous height, the crypt depth, and villous surface area. Compared with that of normal and control rats, the transport and uptake of dipeptide was significantly increased at 3 h post-injury (P < 0.01), peaked at 12 h and declined a bit at 24 h post-injury, and returned to the level of normal and control rats at 72 h and 7 days.

CONCLUSIONS

It is highly suggested that intestinal mucosa apoptosis plays an important role in the pathogenesis of acute gut damage after TBI. Intestinal PepT1 expression could be up-regulated after traumatic brain injury, and maintained the normal level under the condition of serious intestinal damage. Up-regulation of PepT1 may adaptively improve absorption of di- and tripeptides, independent of changes in the mucosal surface area.