1. Oligopeptides: mechanism of renal clearance depends on molecular structure
H Minami, H Daniel, E L Morse, S A Adibi Am J Physiol. 1992 Jul;263(1 Pt 2):F109-15. doi: 10.1152/ajprenal.1992.263.1.F109.
We have investigated the relative contribution of hydrolysis, intact transport and urinary excretion to the renal clearance of Gly-Sar, Gly-Sar-Sar, and Gly-Gly-Sar in fed and starved rats. The results obtained from isolated kidney perfusion studies are summarized as follows: 1) clearance was fastest for Gly-Gly-Sar and slowest for Gly-Sar-Sar, 2) urinary excretion of Gly-Sar-Sar exceeded that of Gly-Gly-Sar or Gly-Sar, 3) there was accumulation of products of hydrolysis of Gly-Gly-Sar in the perfusate but not of Gly-Sar or Gly-Sar-Sar, 4) isolated brush-border and basolateral membranes of renal tubular cells lacked hydrolytic activity against Gly-Sar and Gly-Sar-Sar but possessed hydrolytic activity against Gly-Gly-Sar, 5) an excess amount of Gly-Sar-Sar reduced the rate of clearance of Gly-Gly-Sar by approximately 40% and significantly increased urinary excretion of this peptide, 6) the nonfiltering kidney cleared Gly-Gly-Sar at a rate which was 50% of that of the filtering kidney but did not clear Gly-Sar, and 7) starvation for 96 h was without a significant effect on the renal clearance of either Gly-Sar or Gly-Sar-Sar but significantly reduced the renal clearance of Gly-Gly-Sar and the brush-border membrane hydrolase activity against this peptide. We conclude that the molecular structure determines the affinity of oligopeptides for the membrane transport and hydrolytic systems, which, in turn, determines their efficiency for clearance by the kidney.
2. Experimental and theoretical investigation of the main fragmentation pathways of protonated H-Gly-Gly-Sar-OH and H-Gly-Sar-Sar-OH
Bèla Paizs, Sàndor Suhai, Alex G Harrison J Am Soc Mass Spectrom. 2003 Dec;14(12):1454-69. doi: 10.1016/j.jasms.2003.07.001.
The fragmentation pathways of protonated H-Gly-Gly-Sar-OH and H-Gly-Sar-Sar-OH are investigated by using both computational and experimental techniques. The main goal of these studies is to further investigate which factors determine the branching ratio of the b2-y1 (Paizs, B.; Suhai, S. Rapid Commun. Mass Spectrom. 2002, 16, 375.) and "diketopiperazine" (Cordero, M. M.; Houser, J. J.; Wesdemiotis, C. Anal. Chem. 1993, 65, 1594.) pathways of protonated tripeptides. Protonated H-Gly-Sar-Sar-OH represents a sensitive test for the branching ratio of the b2-y1 and "diketopiperazine" pathways since this ion cannot produce y1 ions on the b(-y1 channel but only b2 ions. Protonated H-Gly-Gly-Sar-OH and H-Gly-Sar-Sar-OH exhibit very different fragmentation behavior under the investigated experimental conditions. The former fragments forming mainly y1 ions (maximum abundance of the b2 and y2 ions is approximately 15%), while the latter produces mainly b2 ions while at larger internal energies the a2, y2, and y1 ions become also moderately abundant. Theoretical modeling and analysis of the main fragmentation pathways indicate that the majority of the b2 and y1 ions of protonated H-Gly-Gly-Sar-OH and the b2 ions of H-Gly-Sar-Sar-OH are formed on the b2-y1 pathway.
3. In vitro evaluation of N-methyl amide tripeptidomimetics as substrates for the human intestinal di-/tri-peptide transporter hPEPT1
Rikke Andersen, Carsten Uhd Nielsen, Mikael Begtrup, Flemming Steen Jørgensen, Birger Brodin, Sven Frokjaer, Bente Steffansen Eur J Pharm Sci. 2006 Jul;28(4):325-35. doi: 10.1016/j.ejps.2006.03.007. Epub 2006 Mar 28.
Oral absorption of tripeptides is generally mediated by the human intestinal di-/tri-peptide transporter, hPEPT1. However, the bioavailability of tripeptides is often limited due to degradation in the GI-tract by various peptidases. The aim of the present study was to evaluate the general application of N-methyl amide bioisosteres as peptide bond replacements in tripeptides in order to decrease degradation by peptidases and yet retain affinity for and transport via hPEPT1. Seven structurally diverse N-methyl amide tripeptidomimetics were selected based on a principal component analysis of structural properties of 6859 N-methyl amide tripeptidomimetics. In vitro extracellular degradation of the selected tripeptidomimetics as well as affinity for and transepithelial transport via hPEPT1 were investigated in Caco-2 cells. Decreased apparent degradation was observed for all tripeptidomimetics compared to the corresponding natural tripeptides. However, affinity for and transepithelial transport via hPEPT1 were only seen for Gly-Sar-Sar, AsnPsi[CONCH(3)]PhePsi[CONCH(3)]Trp, and Gly-Sar-Leu. This implies that tripeptidomimetics originating from tripeptides with neutral side chains are more likely to be substrates for hPEPT1 than tripeptidomimetics with charged side chains. The results of the present study indicate that the N-methyl amide peptide bond replacement approach for increasing bioavailability of tripeptidomimetic drug candidates is not generally applicable to all tripeptides. Nevertheless, retained affinity for and transport via hPEPT1 were shown for three of the evaluated N-methyl amide tripeptidomimetics.
