Spatial expression patterns of peptide transporters in the human and rat gastrointestinal tracts, Caco-2 In Vitro cell culture model, and multiple human tissues

Abstract

This study sought to identify the spatial patterns of expression of peptide transporter 1 (PepT1), peptide transporter 3 (PTR3), peptide/histidine transporter 1 (PHT1), and the human peptide transporter 1 (HPT-1) mRNA in complementary DNA (cDNA) libraries of the human and rat gastrointestinal tracts (GIT), Caco-2 in vitro cell culture model, and in a human multiple tissue panel. Human PTR3 and PHT1 are putative peptide transporters recently discovered. Using sequencespecific primers designed to amplify regions of PepT1, PTR3, PHT1, and HPT-1, we were able to identify the expression of mRNA for each of these transporters in human cDNA panels (Clontech, Palo Alto, CA), the rat GIT, and in Caco-2 cDNA libraries by the polymerase chain reaction (PCR) and Southern Blot analysis. These studies suggest that in the human GIT, PepT1 appears to be localized predominantly in the duodenum, with decreasing expression in the jejunum and ileum. In contrast, PTR3 and HPT-1 were widely expressed in the human GIT, with predominant expression in the different regions of the colon. PHT1 appeared to be expressed in low levels throughout the human GI tract. Interestingly, the mRNAs for all 4 peptide transporters were expressed in Caco-2 cells throughout 30 days of culture. PepT1, PTR3, PHT1, and HPT-1 were also widely expressed in the rat GIT. Human tissue cDNA panel screening suggests that PTR3 and PHT1 are more uniformly expressed, whereas PepT1 and HPT-1 demonstrated sitespecific expression. These results suggest that PepT1, PTR3, PHT1, and HPT-1 all may act to facilitate the diffusion of peptides and peptide-based pharmaceuticals in the GIT. PTR3, PHT1, and HPT-1 expressions in Caco-2 cell monolayers strongly suggest that their function needs to be further elucidated and their contribution to peptide transport not ignored. Taken together, these results demonstrate the potential for molecular biological characterization in localizing active transporter systems that can potentially be targeted for enhancing the absorption of peptide-based pharmaceuticals.

An update on renal peptide transporters

“…This compartmentation could also prevent a premature osmotically induced swelling and rupture of lysosomes (75). The question of whether the lysosomal peptide transporter is PEPT1 or one of the PHT histidine/peptide transporters recently cloned, which are found in lysosomes when expressed heterologously (33,55,74), or a completely new transporter remains to be determined.…”

Significance and Regional Dependency of Peptide Transporter (PEPT) 1 in the Intestinal Permeability of Glycylsarcosine: In Situ Single-Pass Perfusion Studies in Wild-Type andPept1Knockout Mice

“…For example, PEPT2 is found in glial cells and in tissue-resident macrophages of the enteric nervous system (Rühl et al, 2005). Moreover, the peptide/histidine transporters PHT1 and PHT2 have been found in intestinal tissue segments (Herrera-Ruiz et al, 2001), and immunohistochemical analyses have indicated that PHT1 is expressed in the villous epithelium of small intestine (Bhardwaj et al, 2006). However, the functional significance of PEPT2, PHT1, and PHT2 in the intestinal absorption of peptides/ mimetics and peptide-like drugs is uncertain.…”

Oral Absorption, Intestinal Metabolism and Human Oral Bioavailability

“…There are 12 putative α-helical TM domains and a large extracellular loop between the IX and X TM domains, which possess intacellularly localized N-and C-termini (Liang et al 1995;Rubio-Aliaga and Daniel 2008). Herrera-Ruiz et al reported that PepT1 appears to be localized predominantly in the duodenum, with decreasing expression in the jejunum and ileum (Herrera-Ruiz et al 2001).…”