Shiyuan Dong

A novel ACE inhibitory peptide isolated from Acaudina molpadioidea hydrolysate

Body wall protein from the sea cucumber (Acaudina molpadioidea) was hydrolyzed sequentially with bromelain and alcalase. The hydrolysate was fractionated into two ranges of molecular weight (PH-I, >2 kDa; PH-II, <2kDa) using an ultrafiltration membrane bioreactor system. The PH-II brought about a high angiotensin I-converting enzyme (ACE) inhibitory activity. An ACE inhibitory peptide was isolated from the PH-II, using the chromatographic methods including gel filtration, ion-exchange chromatography and reversed phase high-performance liquid chromatography. The purified ACE inhibitory peptide was a novel peptide, showing very low similarity to other ACE inhibitory peptide sequences, and was sequenced as MEGAQEAQGD. It was found that the inhibitory activity of the peptide was intensified by 3.5 times from IC(50) 15.9 to IC(50) 4.5 microM after incubation with gastrointestinal proteases. The ACE inhibitory peptide from A. molpadioidea showed a clear antihypertensive effect in spontaneously hypertensive rats (SHR), at a dosage of 3 microM/kg.

Chemical and Antioxidant Properties of Casein Peptide and Its Glucose Maillard Reaction Products in Fish Oil-in-Water Emulsions

Maillard reaction products (MRPs) were prepared by reacting casein peptides with different concentrations of glucose at 80 °C for up to 12 h. The chemical properties of MRPs and their effects on lipid oxidation in fish oil-in-water emulsions were investigated. Increasing browning development and absorbance in 294 nm in the MRPs caused an increase in DPPH radical scavenging, but a decrease in iron chelation, which could be related to the loss of free amino groups in the peptides. The MRPs produced with longer reaction time or higher glucose concentrations were less effective in inhibiting lipid oxidation in emulsions at pH 7.0 compared to casein peptides alone. However, the antioxidant activity of MRPs in emulsions at pH 3.0 was not decreased by prolonged heating. The bitterness of MRPs was less than that of the original casein peptides, and bitterness decreased with increasing heating time and glucose concentrations. Therefore, the Maillard reaction was a potential method to reduce the bitterness of casein peptides while not strongly decreasing their antioxidant activity.

Formation of ferric oxyhydroxide nanoparticles mediated by peptides in anchovy (Engraulis japonicus) muscle protein hydrolysate.

Nanosized iron fortificants appear to be promising and can be synthesized in a greener way using peptides as biotemplates. Anchovy is a huge underdeveloped source of muscle protein that enhances human nonheme iron absorption. This paper shows that peptides in anchovy ( Engraulis japonicus ) muscle protein hydrolysate (AMPH) mediate the formation of monodispersed ferric oxyhydroxide nanoparticles (FeONPs) with diameters of 20-40 nm above pH 3.0. Peptides in AMPH nucleate iron through carboxyl groups and crystal growth then occur as a result of condensation of carboxylate-ligated hydroxide iron centers, yielding Fe-O-Fe cross-link bonds. Monomers of FeONPs are formed after steric obstruction of further crystal growth by peptide backbones with certain lengths and further stabilized by surface-adsorbed peptides. The iron-loading capacity of peptides in AMPH is up to 27.5 mg iron/g peptide. Overall, the present study provides a greener alternative route to the synthesis of FeONPs.

Antioxidant balance and accumulation of advanced glycation end products after the consumption of standard diets including Maillard reaction products from silver carp peptides

The aim of this research was to investigate the accumulation and excretion of AGEs including fluorescent compounds and N-ε-carboxymethyllysine (CML) in streptozotocin-induced diabetes C57BL/6J mice fed on a diet containing Maillard reaction products (MRPs) from a silver carp peptide-glucose model system at different heating temperatures for the first time, and analyze the relationship between their in vitro antioxidant activity based on DPPH and ORAC assays and in vivo oxidative stress. The in vitro antioxidant activity of MRPs positively correlated with their AGEs level and molecular weight distribution. However, the opposite results were found by malondialdehyde (MDA) and super oxide dismutase (SOD) assays that MRPs from a higher heating temperature could aggravate the oxidative stress of diabetic mice. CML accumulation in serum was aggravated, but changes of MRPs in diets hardly affected CML accumulation in the kidney and liver. Therefore, the high AGEs levels from a diet containing peptide MRPs have negative effects on the oxidative stress of diabetic mice.

Enhancement of non-heme iron absorption by anchovy (Engraulis japonicus) muscle protein hydrolysate involves a nanoparticle-mediated mechanism.

The mechanisms by which meat enhances human absorption of non-heme iron remain unknown. Recently, anchovy (Engraulis japonicus) muscle protein hydrolysate (AMPH) was found to mediate the formation of nanosized ferric hydrolysis products in vitro. The current paper evaluates the effects of AMPH on the bioavailability and the intestinal speciation of non-heme iron in rats, followed by an investigation of cellular uptake pathways of in vitro-formed AMPH-stabilized nanosized ferric hydrolysis products (ANPs) by polarized human intestinal epithelial (Caco-2) cells. The hemoglobin regeneration efficiencies in anemic rats followed the order ferric citrate (9.79 ± 2.02%) < commercial bare α-Fe2O3 nanoparticles (16.37 ± 6.65%) < mixture of ferric citrate and AMPH (40.33 ± 6.36%) ≈ ferrous sulfate (40.88 ± 7.67%) < ANPs (56.25 ± 11.35%). Percentage contents of intestinal low-molecular-weight iron in the groups of FC+AMPH, FeSO4, and ANPs were significantly lower than the corresponding hemoglobin regeneration efficiencies (P < 0.05), providing strong evidence for the involvement of nanosized iron in intestinal iron absorption from FC+AMPH, FeSO4, and ANPs. Calcein-fluorescence measurements of the labile iron pool of polarized Caco-2 cells revealed the involvement of both divalent transporter 1 and endocytosis in apical uptake of ANPs, with endocytosis dominating at acidic extracellular pH. Overall, AMPH enhancement of non-heme iron absorption involves a nanoparticle-mediated mechanism.

Assessing the Antioxidant Activity of the Ultrafiltration Fractions From Silver Carp Protein Hydrolysate by Different Antioxidant Methods

Silver carp protein hydrolysate (SH) was fractionated by 5- and 1-kDa cutoff ultrafiltration (UF) membrane, and three ultrafiltrates were obtained: SHI (>5 kDa), SHII (1–5 kDa), and SHIII (<1 kDa) which were screened for antioxidant activity by five in vitro assays. The SHIII showed higher 2, 2-azobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and oxygen radical absorbance capacity (ORAC) values, inhibiting effects for liposome oxidation induced by Fe3+/VC. The SHII showed higher ferric reducing power (FRAP) and inhibiting effects for liposome oxidation induced by 2, 2′-azobis (2-methylpropionamidine) dihydrochloride (AAPH). However, the SHI showed the highest 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radicals scavenging activity. Therefore, the antioxidant activity of silver carp protein hydrolysates was mainly associated with their molecular weight distribution, and the antioxidant assays used to test different samples gave comparable results.

Novel Natural Angiotensin Converting Enzyme (ACE)-Inhibitory Peptides Derived from Sea Cucumber-Modified Hydrolysates by Adding Exogenous Proline and a Study of Their Structure–Activity Relationship

Natural angiotensin converting enzyme (ACE)-inhibitory peptides, which are derived from marine products, are useful as antihypertensive drugs. Nevertheless, the activities of these natural peptides are relatively low, which limits their applications. The aim of this study was to prepare efficient ACE-inhibitory peptides from sea cucumber-modified hydrolysates by adding exogenous proline according to a facile plastein reaction. When 40% proline (w/w, proline/free amino groups) was added, the modified hydrolysates exhibited higher ACE-inhibitory activity than the original hydrolysates. Among the modified hydrolysates, two novel efficient ACE-inhibitory peptides, which are namely PNVA and PNLG, were purified and identified by a sequential approach combining a sephadex G-15 gel column, reverse-phase high-performance liquid chromatography (RP-HPLC) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/MS), before we conducted confirmatory studies with synthetic peptides. The ACE-inhibitory activity assay showed that PNVA and PNLG exhibited lower IC50 values of 8.18 ± 0.24 and 13.16 ± 0.39 μM than their corresponding truncated analogs (NVA and NLG), respectively. Molecular docking showed that PNVA and PNLG formed a larger number of hydrogen bonds with ACE than NVA and NLG, while the proline at the N-terminal of peptides can affect the orientation of the binding site of ACE. The method developed in this study may potentially be applied to prepare efficient ACE-inhibitory peptides, which may play a key role in hypertension management.

Effect of different cooking conditions on the profiles of Maillard reaction products and nutrient composition of hairtail (Thichiurus lepturus) fillets

Much attention has been given to investigate the formation of Maillard reaction products in thermal processing food due to potential health risks. This study aimed to the profiles of Maillard reaction products (MRPs) and changes of nutrient composition in hairtail (Thichiurus lepturus) fillets prepared by three cooking method: boiling, baking and frying. The Nε-carboxymethyllysine (CML) level ranged from non-detectable to 4.24mg/100g protein and furosine ranged from 4.25 to 20.95mg/100g protein. The levels of CML and furosine in boiled hairtail fillets were much lower than baked and fried ones. The formation of CML was only affected by the cooking method. The changes of the lipid and moisture content, and thiobarbituric acid-reactive substances (TBARS) content in cooked hairtail fillet had different effects on the formation of different stages of Maillard reaction. Furosine level significantly correlated with absorbance in 420nm (r=0.74, p<0.05) and 280nm (r=0.73, p<0.05) and fluorescence Intensity (FI) (r=0.65, p<0.05), but did not correlate with CML. The CML level linearly correlated with the moisture (r=0.79, p<0.01) and lipid content (r=0.73, p<0.05), and the formation of TBARS value (r=0.92, p<0.01), but did not correlate with the FI. Overall, the findings may help to better control the cooking conditions of hairtail meat based on the profiles of MRPs.

Biogenic Polyphosphate Nanoparticles from a Marine Cyanobacterium Synechococcus sp. PCC 7002: Production, Characterization, and Anti-Inflammatory Properties In Vitro

Probiotic-derived polyphosphates have attracted interest as potential therapeutic agents to improve intestinal health. The current study discovered the intracellular accumulation of polyphosphates in a marine cyanobacterium Synechococcus sp. PCC 7002 as nano-sized granules. The maximum accumulation of polyphosphates in Synechococcus sp. PCC 7002 was found at the late logarithmic growth phase when the medium contained 0.74 mM of KH2PO4, 11.76 mM of NaNO3, and 30.42 mM of Na2SO4. Biogenic polyphosphate nanoparticles (BPNPs) were obtained intact from the algae cells by hot water extraction, and were purified to remove the organic impurities by Sephadex G-100 gel filtration. By using 100 kDa ultrafiltration, BPNPs were fractionated into the larger and smaller populations with diameters ranging between 30–70 nm and 10–30 nm, respectively. 4′,6-diamidino-2-phenylindole fluorescence and orthophosphate production revealed that a minor portion of BPNPs (about 14–18%) were degraded during simulated gastrointestinal digestion. In vitro studies using lipopolysaccharide-activated RAW264.7 cells showed that BPNPs inhibited cyclooxygenase-2, inducible nitric oxide (NO) synthase expression, and the production of proinflammatory mediators, including NO, tumor necrosis factor-α, interleukin-6, and interleukin-1β through suppressing the Toll-like receptor 4/NF-κB signaling pathway. Overall, there is promise in the use of the marine cyanobacterium Synechococcus sp. PCC 7002 to produce BPNPs, an anti-inflammatory postbiotic.

A Novel Natural Influenza A H1N1 Virus Neuraminidase Inhibitory Peptide Derived from Cod Skin Hydrolysates and Its Antiviral Mechanism

In this paper, a novel natural influenza A H1N1 virus neuraminidase (NA) inhibitory peptide derived from cod skin hydrolysates was purified and its antiviral mechanism was explored. From the hydrolysates, novel efficient NA-inhibitory peptides were purified by a sequential approach utilizing an ultrafiltration membrane (5000 Da), sephadex G-15 gel column and reverse-phase high-performance liquid chromatography (RP-HPLC). The amino acid sequence of the pure peptide was determined by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) was PGEKGPSGEAGTAGPPGTPGPQGL, with a molecular weight of 2163 Da. The analysis of the Lineweacer–Burk model indicated that the peptide was a competitive NA inhibitor with Ki of 0.29 mM and could directly bind free enzymes. In addition, docking studies suggested that hydrogen binding might be the driving force for the binding affinity of PGEKGPSGEAGTAGPPGTPGPQGL to NA. The cytopathic effect reduction assay showed that the peptide PGEKGPSGEAGTAGPPGTPGPQGL protected Madin–Darby canine kidney (MDCK) cells from viral infection and reduced the viral production in a dose-dependent manner. The EC50 value was 471 ± 12 μg/mL against H1N1. Time-course analysis showed that PGEKGPSGEAGTAGPPGTPGPQGL inhibited influenza virus in the early stage of the infectious cycle. The virus titers assay indicated that the NA-inhibitory peptide PGEKGPSGEAGTAGPPGTPGPQGL could directly affect the virus toxicity and adsorption by host cells, further proving that the peptide had an anti-viral effect with multiple target sites. The activity of NA-inhibitory peptide was almost inactivated during the simulated in vitro gastrointestinal digestion, suggesting that oral administration is not recommended. The peptide PGEKGPSGEAGTAGPPGTPGPQGL acts as a neuraminidase blocker to inhibit influenza A virus in MDCK cells. Thus, the peptide PGEKGPSGEAGTAGPPGTPGPQGL has potential utility in the treatment of the influenza virus infection.