A metabolite of peptide IRW plays a key role in its blood pressure lowering activity

Food-derived bioactive peptides hold vast potential for improving human health. However, food-derived bioactive peptides are susceptible to degradation and metabolism during digestion, absorption, and circulation. We previously identified the first food-derived angiotensin-converting enzyme 2 (ACE2) up-regulatory peptide IRW. Oral administration of IRW to animals has consistently demonstrated its in vivo efficacy. This study aimed to investigate the pharmacokinetic characteristics of IRW and identify the metabolites responsible for its antihypertensive activity in spontaneously hypertensive rats (SHRs). As IRW is rapidly metabolized, we performed a time-course metabolomic study to identify the metabolites that are responsible for the antihypertensive activity of IRW.

Rats were administrated 100 mg IRW/kg body weight via intragastric or intravenous routes to SHRs, and blood was collected at 0, 5, 10, 20, 30 min, 1, 3, and 6 h. Dansylation LC-MS was used to analyze IRW in blood. One-compartmental modeling was employed to determine other pharmacokinetic parameters. Acute blood pressure lowering activity in SHRs was measured using telemetry transmitters. Plasma metabolomics were analyzed using LC-MS after derivation of the plasma samples by chemical isotope labeling. Effect of IRW, single amino acid W, or kynurenine (identified metabolite) on ACE2 gene expression was studied in cells. Effect of dipeptide IR and W on blood pressure lowering activity was further studied in SHR.  

IRW’s bioavailability (F%) was determined to be 11.7%, and the half-lives were 7.9 and 28.5 min for gavage and injection, respectively. Time-course metabolomics revealed a significant increase in kynurenine, a tryptophan metabolite, after IRW administration. Kynurenine also increased ACE2 level in cells. W, but not IR, lowered SHR’s blood pressure, attributed to ACE2 upregulation. Our study supports the key role of tryptophan and its metabolite, kynurenine, in IRW’s blood pressure lowering effects.