Oligopeptide uptake

Localization of the peptide transporter PEPT2 in the lung implications for pulmonary oligopeptide uptake. Am J Pathol 2001 158(2)707-714. 

This may arise, for example, when a dipeptide containing L-lysine and a catabo-lizable amino acid such as L-alanine is taken up and hydrolyzed by constitutive di- and oligopeptide uptake and hydrolase systems [39, 40]. Synthesis of LysE is controlled by LysG and occurs only if the intracellular L-lysine concentrations exceeds a threshold of about 35 mM [42]. L-Lysine export could be improved fivefold by overexpression of lysE [39,40]. Expression of lysE under control of an L-lysine riboswitch was also applied (see below [43]). 

In this work we will focus on the use of the cubic phase as a delivery system for oligopeptides - Desmopressin, Lysine Vasopressin, Somatostatin and the Renin inhibitor H214/03. The amino acid sequences of these peptides are given in Table I. The work focuses on the cubic phase as a subcutaneous or intramuscular depot for extended release of peptide drugs, and as a vehicle for peptide uptake in the Gl-tract. Several examples of how the peptide drugs interact with this lipid-water system will be given in terms of phase behaviour, peptide self-diffusion, in vitro and in vivo release kinetics, and the ability of the cubic phase to protect peptides from enzymatic degradation in vitro. Part of this work has been described elsewhere (4-6). 

In cell lines, the organic anion transporters (OAT and OATP) have been identified and cloned into cells of kidney origin such as LLC-PK1, MDCK, HK-2, and Caco-2 [129]. The most well-known uptake transporters, which transport the substrate over the membrane into the organism are the amino acid- [35, 42, 139] and oligopeptide-carriers (PepTl and PepT2) [139-142]. These two transporter families are abundantly expressed in the small intestine of most animals, and can therefore be involved in the absorption process of pharmaceutical drugs. The PepTl is expressed in the cell lines Caco-2 and HT-29 [140-142]. 

Pan, Y., et al. Expression of a cloned ovine gastrointestinal peptide transporter (oPepTl) in Xenopus oocytes induces uptake of oligopeptides in vitro. J. Nutr. 2001, 131, 1264-1270. 

Kramer, W., et al. Interaction of renin inhibitors with the intestinal uptake system for oligopeptides and beta-lactam antibiotics. Biochim. Biophys. Acta 1990, 1027, 25-30. 

B., Frokjaer, S., Influence of oligopeptide transporter binding affinity upon uptake and transport of D-Asp(OBzl)-Ala and Asp(OBzl)-Sar in filter grown Caco-2 monolayers, Int. J. Pharm. 1997, 156, 219-228. 

An oligopeptide of relative molar mass 1600 that binds Fem and functions to enhance the cellular uptake of Fe has been isolated from mouse cells.51 The peptide also binds Co11 but does not enhance the uptake of this metal. The peptide has been referred to as the siderophore-like growth factor (SGF). There is also a proposed Cr-chelating peptide this glucose tolerant factor is essential for the utilization of Cr in the proper functioning of insulin in cells.72 Whilst Zn11 is normally associated... 

Uptake studies for peptides have been performed by adding the compound to the apical side of the filter (pH 6.5 for optimal function of oligopeptide transporter). The pH at the basolateral side was 7.4. After a preincubation period (10 min, 37 °C) cells should be washed and incubated for 15 min (or for a shorter time period) with the compound under evalation. After incubation period medium is removed, cells are washed 3 times with ice-cold pH 7.4 buffer to stop further uptake and to remove unbound compound (for details see Tamura et al. 1996). Cells should be scraped and dissolved in ice-cold buffer. If a radioactive compound is studied, cells and filters are dissolved in a Ready-Safe scintillation cocktail and radioactivity is determined in a liquid scintillation counter. Alternatively, for non-radioactive compounds LC-MS or HPLC detection is recommended. 

Krznaric, E. (2004). Uptake of amino acids and oligopeptides in mycorrhizal Pinus sylvestris. Unpublished MS thesis, Katholieke Hogeschool Limburg. 

In recent years, there has been increasing awareness regarding the importance of transporters in the absorption and disposition of NMEs. While the major portion of NMEs or marketed drugs traverse cell membranes by passive diffusion, there are numerous examples where the involvement of specialized transport mechanisms has been demonstrated. Examples include the role of oligopeptide transporters in the intestinal absorption of P-lactam antibiotics, angiotensinconverting enzyme (ACE) inhibitors, and novel NMEs as well as the role of P-glycoprotein (P-gp) in the secretion of molecules into the intestine [11,77—79]. Transfection of cells with the transporter protein of interest has permitted the evaluation of precise cellular mechanisms of uptake and transport of NMEs. Transfected cell lines by definition are tailor-made to overexpress the protein of... 

The digestion of proteins begins in the stomach, where the low pH denatures the proteins so that they are more easily hydrolyzed by the enz)une pepsin. They are further degraded in the small intestine by tiypsin, ch)miotiypsin, elastase, and other proteases. The products of protein digestion—amino acids and short oligopeptides—are taken up by the cells lining the intestine. This uptake also involves an active transport mechanism. 

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