Purification, Characterization And Antihypertensive And Hepatoprotective Effects Of Bioactive Peptides Derived From Spirulina Platensis

The present study was performed to isolate and purify angiotensin converting enzyme (ACE) inhibitory peptides from enzymatic digests of Spirulina platensis by ultra-filtration, gel filtration chromatography and reverse-phase high-performance liquid chromatography. The purified peptides were identified by mass spectrometry and amino acid sequencing, and were determined for the inhibition pattern and the stability in vitro. The in vivo antihypertensive effects and regulation mechanism on the renin-angiotensin system (RAS) were also investigated in spontaneous hypertensive rats (SHR) by methods of Real-Time PCR and Enzyme-linked immunosorbent assay. Furthermore, the hepatoprotective effects and the regulation mechanism of dietary Spirulina platensis and its enzymatic digests against D-galactosamine (D-GalN) or acetaminophen (APAP) induced hepatitis were investigated in ICR mice and Wistar rats.The results indicated that the enzymatic digests ranging in 0 - 3,000 D had the highest ACE inhibitory activity. Two potent ACE inhibitory peptides with IC₅₀ values of 5.77±0.09μmol/L and 27.36±0.14μmol/L were obtained from the Alcalase and papain digests, and were identified as Ile-Gln-Pro and Val-Glu-Pro, respectively. Both of the peptides were determined as non-competitive inhibitors with K_i values of 7.61±0.16μmol/L and 23.59±0.54μmol/L respectively, and kept their inhibitory activities well after incubation with main gastrointestinal proteases.In vivo experiments in SHRs indicated that the least effective doses of Ile-Gln-Pro and Val-Glu-Pro were 2.5 mg/kg body weight (BW) and 5 mg/kg BW respectively, and the antihypertensive effects were accompanied with their regulation on major components in the RAS. Compared with Captopril, both of the peptides exhibited more potent activities in vivo than in vitro, and maintained the best antihypertensive effects longer.Furthermore, dietary Spirulina platensis and its enzymatic digests could effectively suppress the acute liver injuries induced by D-GalN or APAP in ICR mice and Wistar rats, and the hepatoprotective effects were accompanied with their regulation on lipid peroxidation in the liver as well as expressions of the proinflammatory cytokine IL-18 and the hepatic RAS components.The present work purified potent ACE inhibitory peptides from Spirulina platensis for the first time, and innovatively investigated the antihypertensive and hepatoprotective effects of Spirulina platensis and the regulation on expressions of IL-18 and the RAS components. The results suggested Spirulina platensis would be of great prospects as an ingredient of functional foods or medicines in treatment of hypertension and liver injuries.