Hypertension is known as an important factor in cardiovascular disease. An angiotensin-I-converting enzyme (ACE) inhibitor is one of the synthetic drugs that is widely used to control hypertension. Here, we have prepared and investigated the ACE inhibitory peptide from Ruditapes philippinarum fermented with Bacillus natto. The fermented product obtained under optimized fermentation conditions exhibited ACE inhibitory activity. The ACE inhibitory peptides were purified by ultrafiltration, gel filtration chromatography and RP-HPLC, sequentially. A novel peptide with high ACE inhibitory activity (IC50 of 8.16 μM) was isolated and the amino acid sequence was identified to be Val-Ile-Ser-Asp-Glu-Asp-Gly-Val-Thr-His (VISDEDGVTH) by LC-MS/MS. The Lineweaver-Burk plots suggested that VISDEDGVTH acts as a competitive inhibitor against ACE. Our in vitro study indicated the stability of VISDEDGVTH against gastrointestinal proteases. An in vivo study in rats proved the significant anti-hypertension effect of the peptide. Furthermore, the cellular mechanism of VISDEDGVTH moderating hypertension was investigated. We found that VISDEDGVTH enhanced the release of NO, inhibited the secretion of EF-1, and scavenged ROS in human vascular endothelial cells. Our study suggests that VISDEDGVTH serves as an anti-hypertension and anti-inflammatory drug and as a beneficial ingredient in functional foods and pharmaceuticals.

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To understand the mode of action of low molecular weight phlorotannins (LMPs) from Sargassum thunbergii against Vibrio parahaemolyticus, effects of LMPs on the growth curve and the content changes of some substances in culture media were investigated, and those on morphological and ultra-micro structure were also observed by scanning electron microscope and transmission electron microscopy. The results showed that LMPs inhibited thalli growth at logarithmic phase and damaged the cell membrane and cell wall of tested bacteria which led to the leakage of cytoplasm and the deconstruction of membrane permeability. The present study indicates that LMPs as natural products in seaweeds deserve further investigation for food safety control and aquacultural drugs.