Antihypertensive and Antioxidant Properties of Chicken Skin Protein Hydrolysates: In vitro, in vivo, and Metaboloics Studies
Onuh, John Oloche
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The objective of this work was to produce bioactive peptides from the enzymatic hydrolysis of chicken skin proteins that could be used to treat hypertension, oxidative stress and associated health conditions using a metabolomics approach. Enzymatic hydrolysis of chicken thigh and breast muscle skin proteins was carried out using alcalase or a combination of pepsin/pancreatin (PP) at 1–4% enzyme concentrations. Chicken skin protein hydrolysates (CSPH) were each fractionated by membrane ultrafiltration into different molecular weight peptides (<1, 1–3, 3–5 and 5–10 kDa). Investigation of their in vitro antihypertensive and antioxidant activities showed that alcalase hydrolysates had significantly (p < 0.05) higher ACE-inhibitory activity compared to PP hydrolysates. ACE inhibition was inversely related to size of ultrafiltration membrane peptides. Renin-inhibitory activity varied from 15–36%, and was dependent on the type of protease; PP hydrolysates showed significantly (p < 0.05) higher inhibition than alcalase hydrolysates. CSPHs also significantly (p < 0.05) scavenged antioxidant radicals, increasing with enzyme concentration but decreased as peptide size increased. Kinetics studies revealed that peptide-dependent enzyme inhibition pattern was mostly of the mixed-type for both ACE and renin. Short-term (24 hr) oral administration of 100 mg peptides/kg body weight to spontaneously hypertensive rats (SHRs) led to maximum systolic blood pressure (SBP) reduction of –32.67 and –31.33 mmHg after 6 h for chicken thigh skin hydrolysate and chicken breast skin hydrolysate, respectively. During a 6-week feeding trial, CSPH at 1.0 and 0.5% feed substitutions had significant (p<0.05) antihypertensive effects in SHRs (-36 and -31 SBP reductions, respectively). SBP reduction was directly related to lower plasma ACE but not renin activity. Plasma total antioxidant capacity of the rats was also high. Metabolomics analysis revealed several metabolites with significant changes (≥ 2-fold changes, p < 0.05) in urine and plasma of SHRs fed CSPH, such as Symmetric Dimethylarginine (SDMA), N2-acetyl-L-ornithine, buthionine sulfoximine, uric acid, Vitamin E succinate, L-isoleucine and phospholipids which may be considered important biomarkers/pathways for hypertension and oxidative stress. We conclude that CSPHs may be used as ingredients to formulate functional foods and nutraceuticals for the management of oxidative stress and hypertension-related diseases.