Characterization And Biological Activity Of Bioactive Peptides From Egg White Protein

Proteins are important components of foods and ingredients of food products. Inaddition to their nutritional role, proteins can act as functional food ingredients，including antihypertension, antioxidant, and anti-diabetic properties. Research carriedout to produce these foods has paid special attention to the study of the physiologicalrole played by dietary proteins. There are certain fragments within the sequence offood proteins that may show biological activity once released by hydrolysis. Thesefragments, known as bioactive peptides, can be produced in vivo by the action ofgastrointestinal enzymes and can also be obtained in vitro using specific enzymes, orduring the preparation of certain foods. Peptide research has contributed greatly tovarious areas of human health. The production of eggs in china is first in theworldwide. The egg white proteins include ovalbumin, ovotransferrin, ovomucoid,ovomucin, lysozyme, avidin, ovoinhibitor, ovomacroglobulin, and cystatin. Previousresearches suggested that hydrolysates of egg white proteins exhibited diverse ofphysiological properties, including novel antimicrobial activities, antiadhesiveproperties, immunomodulatory, anticancer, and antihypertensive activities, antioxidantproperties. Several biological activities have now been associated with hydrolysatesfrom egg white proteins, highlighting the importance of egg and egg components inhuman health and in disease prevention and treatment.Following our previous work,19bioactive peptides have been isolated and purifiedby proteomics technology including chromatographic, tandem mass spectrometry.Subsequently, The secondary structures of those peptides, i.e., α-helix, β-angle,β-sheet, random coil, and other information, were performed using circular dichroism(CD) and Fourier transform infrared spectroscopy (FTIR). In vitro angiotensinconverting enzyme inhibitory activity, α-glucosidase inhibitory activity, α-amylaseinhibitory activity and anti-thrombin activity of those peptides from egg whiteproteins were measured, aimed to screen bioactive peptides with high activity. After the single oral administration, short-term oral administration and long-termadministration with peptides from egg white proteins for rats, target proteinsconcerntration from serum and the gene expression levels of kidney were evaluatedby methods of Real-Time PCR and Enzyme-linked immune assay. At the same time,behavior of rats administrated with peptides from egg white proteins was studied bythe behavioral medicine assay.Firstly, egg white proteins were hydrolyzed and isolated, and the purified fractionof hydrolysates was characterized by tandem mass spectrometry. The result suggestedthat fraction of hydrolysates was identified and peptides sequence of the fraction wereRVPSLM, TPSPR, DLQGK, AGLAPY, RVPSL, DHPFLF, HAEIN, QIGLF,HANENIF, VKELY, TNGIIR, KLPGF, EAGVD, EVSGL, NVLQPS, QITKPN,LEPINF, AEAGVD and ANENIF, respectively. Those peptides consists of5-6aminoacid residues, and the molecular weight distribution of peptides range between500-850Da. Our result showed that α-helical, β-folding and β-angle components ofthose peptides were below6%by the Fourier transform infrared spectroscopy andcircular dichroism analysis.Subsequently, in vitro angiotensin converting enzyme inhibitory activity, α-amylaseinhibitory activity, α-glucosidase inhibitory activity and inhibiting the activity againstthrombin activity of thsoes peptides were performed aimed to obtain high activitypeptides. Research have shown that QIGLF and RVPSL exhibited high activityagainst angiotensin converting enzyme, and found a novel angiotensin convertingenzyme inhibitory peptides, i.e., TNGIIR, with IC5070μmol/L; α-amylase inhibitoryactivity and α-glucosidase inhibitory activity of those peptides were measured, resultsshowed that bioactive peptide RVPSLM, TPSPR, KLPGF and NVLQPS performedhigher α-glucosidase inhibitory activity, and their values of IC50responsed to23.07μmol/L,40.02μmol/L,59.5μmol/L and100.0μmol/L, respectively. Peptide KLPGFshowed high α-amylase inhibitory activity with an IC50of120.0±4.0μmol/L. resultsalso suggested that peptide RVPSL was potential to exhibit high anti-thrombinactivity.In addition, the present study was designed to evaluate the effect of RVPSL,QIGLF and TNGIIR orally administered on the anxiety-related behavior. Our workassessed the anxiolytic-like effects of those peptides after an oral administration in spontaneously hypertensive rats faced to the same behavioral situations using elevatedplus maze. The results showed that compared to negative control, the number ofentries into the open arms significantly decreased by QIGLF and Captopril treatment,but the number of entries did not decreased by TNGIIR and RVPSL treatment.Followed by the Morris water maze test and avoiding darkness test, the resultssuggested that egg whited derive peptides, i.e., RVPSL，QIGLF, and TNGIIR, did notaffect the ability of learning and memory for rats.Finally, the research focused on the antihypertensive effect of peptides (i.e.,RVPSL，QIGLF, and TNGIIR) on mRNA Expression and physiological parameter ofspontaneously hypertensive rats (SHRs), after sigle oral administration, short-termadministration, and long-term administration, respectively. In addition, Kidney mRNAlevels of renin, ACE, and AT1and AT2receptors were detected by real-time PCR;besides, Ang I, Ang II, renin, and aldosterone concentrations of serum were alsomeasured. Our results indicated that blood pressure of treatment group administratedwith RVPSL (50mg/kg bw) and QIGLF (50mg/kg bw) to spontaneous hypertensiverats for long-term decreased significantly by30mmHg compared to the negativegroup, but which was still difference from that of captopril treatment group (withdecrease by50mmHg). At the same time, Serum Ang II, renin, and aldosteroneconcentrations of group treated with RVPSL were reduced compared to that of thenegative group. Subsequently, Kidney mRNA levels of renin, ACE, and AT1receptorof RVPSL treated group decreased significantly compared to that of negative group.our results indicated that the peptide RVPSL affected the expression of major RAScomponents by downregulating the ACE and AT1receptor while upregulating the AT2receptor in the kidney or serum of SHRs. Our findings suggested that RVPSL mightbe of potential use in the treatment or prevention of hypertension.This study was able to investigate the in vivo bioactivity of the peptide from egg protein and was helpful to clarify the mechanism of bioactive peptides. The researchpossesses highly academic value and will enhance economic returns for enterpriseseventually.