title: The bioactive peptide cyclo(His-Pro) may be absorbed following ingestion of nutritional supplements that contain it.
abstract: OBJECTIVE
  Food contains a number of peptides with potential bioactivity. We previously found ng/mliter to mcg/mliter quantities of cyclo(His-Pro)-like immunoreactivity in a number of foods and nutritional supplements. A number of activities have been attributed to cyclo(His-Pro) (CHP), including appetite inhibition and inhibition of insulin secretion in vitro. We wondered whether the cyclo(His-Pro)-like immunoreactivity present in nutritional supplements might be absorbed and, if so, whether parameters of insulin secretion would be altered.
  
  
  METHODS
  After performing a pilot study which suggested some common nutritional supplements contain CHP, a follow-up study was done to confirm and expand the findings of the pilot study. Eight fasting volunteers ingested approximately 250 mL of a CHP-containing supplement one day, and then an equienergetic CHP-free supplement the next.
  
  
  RESULTS
  Blood drawn for CHP, insulin, glucose, and C-peptide a number of times on both days revealed that when volunteers ingested CHP-containing supplements, CHP levels at 120 minutes were significantly higher than baseline (7.69 +/- 0.50 pmol/mL vs. 9.18 +/- 0.48 pmol/mL; p = 0.011 in the CHP group and 7.90 +/- 0.85 pmol/mL vs. 7.22 +/- 0.73 pmol/mL, p > 0.3 in the CHP-free group) and significantly higher than levels achieved when they drank CHP-free supplements. Levels of glucose, insulin, and C-peptide were not different in the two groups.
  
  
  CONCLUSIONS
  CHP in nutritional supplements may be absorbed when ingested orally and does not grossly affect glucose or parameters of insulin secretion.
authors.affiliation: Department of Medicine, LSU Medical Center, New Orleans 70112, USA.
authors.forename: H
authors.initials: H
authors.lastname: Mizuma
authors.forename: B Y
authors.initials: BY
authors.lastname: Legardeur
authors.forename: C
authors.initials: C
authors.lastname: Prasad
authors.forename: C W
authors.initials: CW
authors.lastname: Hilton
mesh_terms: D000042:Absorption; D000328:Adult; D000975:Antioxidants / Q000008:administration & dosage / Q000493:pharmacokinetics*; D002241:Carbohydrates / Q000493:pharmacokinetics; D019422:Dietary Sucrose; D005260:Female; D005526:Food, Formulated; D006801:Humans; D010456:Peptides, Cyclic / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D010865:Pilot Projects; D010879:Piperazines / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*
chemical_list: D000975:Antioxidants; D002241:Carbohydrates; D019422:Dietary Sucrose; D010456:Peptides, Cyclic; D010879:Piperazines; C082131:Ensure formulated food; C015924:histidyl-proline diketopiperazine