Preparation and therapeutic biological activities of hydrolysate mixture produced from frog (Rana tigrina) skin using protease

Abstract

Importance of the work: Nowadays, a noncytotoxic hydrolysate containing multiple biological
activities is an ideal product for discovering vital bioactive peptides for use in the production
of nutraceuticals and pharmaceuticals and for developing alternative treatments for metabolic
syndrome.
Objectives: To determine the biological activities and bioactive peptides involved in the hydrolysate
mixture (HFS) from frog (Rana tigrina) skin.
Materials and Methods: The FHS was investigated for its 1,1-diphenyl-2-picrylhydrazyl (DPPH)
and 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radical scavenging activities,
its angiotensin I-converting enzyme (ACE) inhibitory (ACE-I) activity, antimicrobial activities
and toxicity to fibroblast (HS 68) cells. Connections of peptides with the ACE in the HFS were
determined using high-performance liquid chromatography-tandem mass spectrometry (HPLCMS/MS) and the docking method.
Results: The HFS confirmed the DPPH and ABTS scavenging activities. Notably, the HFS inherited
ACE-I activity at a significant half-maximal inhibitory concentration value of 85.47 mg/mL but did
not involve antimicrobial actions or inhibit the growth of HS 68 cells at contents of 0.5 mg/mL or
10 mg/mL. Four peptides (F1, F2, F3, F4) in the HFS were determined for their amino acid sequences
using HPLC-MS/MS. The docking results between these peptides with the ACE model improved
insights into the structure-activity relationship of the ACE inhibitory peptides. Notably, F1 contained
vital residues for forming the most hydrogen bonds, and a Pi-alkyl interaction resulted in effective
ACE-I activity based on its binding energy (-10.9 kcal/mol) compared to captopril (-5.4 kcal/mol).
Main finding: All results suggested effective enzymatic hydrolysis had produced HFS containing
potential value for its biological activity and non-toxic ability; the novel bioactive peptides found
in the HFS could be applied as scaffolds for more intensive research on therapeutic peptides against
ACE and contribute to treating hypertension.