Role and location of PEPT1 and PEPT2 transporters
PEPT1 and PEPT2 belong to the SLC transporter family and are the main peptide transporter within the body being responsible for the proton-coupled transport of dipeptides and tripeptides. Their main function is in the absorption of dietary nitrogen in the small intestine (PEPT1) and reabsorption of nitrogen from the glomerular filtrate in the renal proximal tubule (both PEPT1 and PEPT2). Despite these common functionalities, some key differences exist between these 2 transporters as detailed below:
- Firstly, localisation of PEPT1 is predominantly on the brush border of the small intestine and to a lesser extent on renal epithelial cells whereas PEPT2 is widely distributed in the body yet is mainly located in the renal epithelial cells.
- Secondly, PEPT1 is a low affinity, high capacity transporter whereas PEPT2 is a high affinity, low capacity transporter. Although both transporters accept a large number of substrates, PEPT2 is believed to have a narrower substrate range than PEPT2.
Application of PEPT1 transporter in drug delivery
PEPT1 is much more well characterised compared to PEPT2. This is in part due to the fact that uptake by PEPT1 is a popular route for prodrug design for drug delivery. For example, prodrugs which have amino acids as pro-moieties have been designed as substrates of PEPT1 to improve oral absorption and bioavailability. The antivirals, valacyclovir and valganciclovir are examples where this has been successful.
Regulation of PEPT1 transporter and its role in intestinal inflammation
A number of factors have been reported to regulation of PEPT1 including altered dietary intake and increased dietary protein. There is also evidence of the PEPT1 transporter playing a role in the pathogenesis of intestinal inflammation and inflammatory bowel disease. It is believed that the changes in expression of PEPT1 in the colon can lead to uptake of bacterial peptides. These peptides can activate pro-inflammatory signalling pathways leading to the release of cytokines and chemokines and ultimately an enhanced inflammatory response.
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