title: pGlu-L-Dopa-Pro: a tripeptide prodrug targeting the intestinal peptide transporter for absorption and tissue enzymes for conversion.
abstract: OBJECTIVE
  The purpose of this study is to investigate the characteristics of pGlu-L-Dopa-Pro as a prodrug of L-Dopa.
  
  
  METHODS
  pGlu-L-Dopa-Pro and L-Dopa-Pro were synthesized using the standard procedures of peptide synthesis. The conversion of pGlu-L-Dopa-Pro to L-Dopa was studied using pyroglutamyl aminopeptidase I and prolidase. With rats as the animal model, the stability of pGlu-L-Dopa-Pro in intestinal homogenates was determined, then the transport characteristics of pGlu-L-Dopa-Pro were studied using in-situ perfusion and Ussing chambers.
  
  
  RESULTS
  pGlu-L-Dopa-Pro, relatively stable in intestinal homogenates and intestinal fluid, had a dimensionless permeability of 1.8 at 0.04 mM. Its intestinal permeability was significantly inhibited by 20 mM captopril, by a mixture of dipeptides, 80 mM Gly-Gly and 5 mM Gly-Pro, and by 2 mM cephradine. Further, in Ussing chambers, its mucosal to serosal permeability decreased dramatically with concentration. Conversion studies showed that pGlu-L-Dopa-Pro was degraded by pyroglutamyl aminopeptidase I, an enzyme releasing the N-terminal pyroglutamic acid, with Vmax and Km of 0.6 mumole/min/g protein and 21 mM, respectively, and that L-Dopa-Pro was degraded by prolidase with Vmax and Km of 44 mumole/min/g protein and 0.48 mM, respectively.
  
  
  CONCLUSIONS
  This tripeptide, a potential prodrug of L-Dopa, is absorbed by the intestinal peptide transporter, is relatively stable in the gut wall, and is converted to L-Dopa by peptidases with the cleavage by pyroglutamyl aminopeptidase I to L-Dopa-Pro as the rate limiting step.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001711:Biotransformation; D015820:Cadherins; D002352:Carrier Proteins / Q000378:metabolism*; D004229:Dithiothreitol / Q000494:pharmacology; D015259:Dopamine Agents / Q000493:pharmacokinetics* / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D006868:Hydrolysis; D007408:Intestinal Absorption; D007980:Levodopa / Q000031:analogs & derivatives* / Q000493:pharmacokinetics* / Q000494:pharmacology; D008297:Male; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000493:pharmacokinetics* / Q000494:pharmacology; D011355:Prodrugs / Q000493:pharmacokinetics*; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D015820:Cadherins; D002352:Carrier Proteins; C490586:Cdh17 protein, rat; D015259:Dopamine Agents; D026901:Membrane Transport Proteins; D009842:Oligopeptides; D011355:Prodrugs; C067802:intestinal peptide-proton cotransporter; C096973:pyroglutamyl-L-DOPA-proline; D007980:Levodopa; D004492:Edetic Acid; D011761:Pyrrolidonecarboxylic Acid; D004229:Dithiothreitol