Antihypertensive Effect And Absorbtion Of Rice Peptide

Rice protein extracted by alkali was hydrolyzed using alcalase and trypsin toobtain rice peptide (RP). Its absolute molecular weight, amino acid compositions,peptide content, angiotensin-I converting enzyme inhibitory activity and antioxidantactivity were determined in the research. The antihypertensive effects of rice peptidein vivo were evaluated using the model of spontaneously hypertensive rats (SHR) andwistar kyoto (WKY). SHR and WKY were administrated orally once and long-term,respectively. The human colon adenocarcinoma cell line (Caco-2) monolayer wasused to explore the absorption of synthesized tripeptide and rice peptide in humanintestinal.The absolute molecular weight of rice peptide mainly distributed from549to1158Da. The composition proportion of amino acids was abundant, and essentialamino acids were35.610g/100g. The hydrophobic amino acids were45.200g/100g,and the amino acid in the largest content was glutamic acid, which accounted for16.100g/100g. The peptides in rice hydrolysate were83.84±1.44percent. Ricepeptide could eliminate radicals effectively and the IC50value of DPPH radical was1.170mg/mL with ORAC value of1568.006μmol Trolox/g. It also had strong ACEinhibitory activity with IC50value of0.057mg/mL.After single oral administration, the systolic blood pressures (SBP) of allspontaneous hypertension rats (SHR) began to drop and reached the lowest at6st hour.The administration of RP (100mg/kg) produced the maximal decrease of SBP,followed by RP (50mg/kg) and RP (20mg/kg). However, the antihypertensive activityof captopril was better than that of RP (100mg/kg). RP (100mg/kg) had the sameantihypertensive effect as the captopril (P<0.05) while RP (20mg/kg) antihypertensiveeffect was not significant (P>0.05). Besides, the SBP of WKY treated with captoprillowered significantly (P<0.05). RP (100mg/kg) had no antihypertensive effect onWKY. The SBP of SHR and WKY returned to the initial level after24h. The resultsof long term oral administration experiments showed that the SBP of SHR treatedwith RP (100mg/kg) and captopril was lowered significantly (P<0.05) after6weeks.The SBP of SHR dropped for18.8mmHg,17.1mmHg, and8.2mmHg in captopril, RP(100mg/kg), and RP (50mg/kg) group respectively after6weeks’ administration.Meanwhile, the SBP of WKY treated with captopril was lowered significantly(P<0.05) while the SBP of WKY treated with RP (100mg/kg) had not changed almost. Based on antihypertensive effect of RP, the antihypertensive mechanism of RPwas explored. There was no significant difference in rennin level among all the rats’groups. After6-week treatment of captopril10mg/kg in SHRs, the ACE level wasdecreased significantly (P<0.01), while SHRs administrated with RP100and50mg/kg was decreased less significantly (P<0.05). Plasma Ang II in SHRsadministrated with captopril10mg/kg was decreased significantly (P<0.05). All RPgroups’ Ang II level was decreased when the RP dose was increased, but the changeswere not significant. After long-term administration of captopril10mg/kg, RP100and50mg/kg, plasma NO of these groups was increased dramatically and ACEactivity of these groups was decreased dramatically (P<0.01). After long-termadministration of captopril10mg/kg in WKYs, plasma NO of the group wasincreased dramatically (P<0.01), and Ang II was decreased significantly (P<0.05) aswell as ACE activity. Besides, captopril had no effect on ACE level. The changes ofleft ventricle/body weight (LV/BW) among these groups showed that captopril andRP (100mg/kg) could lower rats’ SBP, and they inhibited left ventricular hypertrophyto some extent. The level of rennin, ACE, AngⅡ, NO and ACE activity indicated thatthe antihypertensive mechanism of RP was associated with regulating NO andrennin-angiotensin system (RAS).Caco-2cell model was established to evaluate the absorption of RP andsynthesized tripeptide in this study. Being cultured in transwell inserts for21days,Caco-2cell transepithelial electrical resistane (TEER) values increased to409Ω/cm2,and alkaline phosphatase (AKP) was focused on the apical side (AP) mostly.Futhermore, the apparent permeability (Papp) value of fluorescein disodium salt was1.9810-7cm/s. Judging from those indicators, this monolayer model was verysuitable for absorption research. VNP (Val-Asn-Pro) and rice peptide safeconcentrations for Caco-2cell were1mg/mL and2mg/mL. The transport of VNP inrice peptide and synthesized VNP was increased time-dependent gently and linearly. Itindicated that there were no inhibitors for VNP transport in rice peptide. Meanwhile,VNP transport was dose-dependent. The Papp of VNP was3.8810-6cm/s, andtherefore VNP was a medium-absorption drug with the absorption rate of20%-70%.Gly-Pro and wortmannin made no difference to VNP transport while sodiumdeoxycholate could enhance VNP transport significantly (P<0.01). The results showedthat VNP was absorbed across intestinal epithelial cells by paracellular diffusionmainly.