Identification and Characterization of Dipeptidyl Peptidase-IV Inhibitory Peptides from Oat Proteins

An Update on Dipeptidyl Peptidase-IV Inhibiting Peptides

Diabetes is a chronic metabolic disorder. According to the International Diabetes Federation, about 537 million people are living with diabetes. The two types of diabetes are type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM), among which the population affected by T2DM is relatively higher. A major reason for T2DM is that insulin stimulation is hampered due to the inactivation of incretin hormones. Dipeptidyl peptidase-IV (DPP-IV) is a serine protease that is directly involved in the inactivation of incretin hormones, e.g., glucagon-like peptide-1 (GLP-1). Therefore, the inhibition of DPP-IV can be a promising method for managing T2DM, in addition to other enzyme inhibition strategies, such as inhibition of α-amylase and α -glucosidase. Currently, about 12 different gliptin drugs are available in the market that inhibit DPP-IV in a dose-dependent manner. Instead of gliptins, 'peptides' can also be employed as an alternative and promising way to inhibit DPP-IV. Peptide inhibitors of DPP-IV have been identified from various plants and animals. Chemically synthesized peptides have also been experimented for inhibiting DPP-IV. Most peptides have been analysed by biochemical assays, whereas some in vitro assays have also been reported. Molecular docking analysis has been applied to comprehend the mechanism of inhibition. In this review, certain aspects of natural as well as synthetic peptides are described that have been proven to inhibit DPP-IV.

Dipeptidyl Peptidase IV Inhibitory Peptides from Chickpea Proteins (Cicer arietinum L.): Pharmacokinetics, Molecular Interactions, and Multi-Bioactivities

Chickpea (Cicer arietinum L.) peptides can inhibit dipeptidyl peptidase IV (DPP-IV), an important type 2 diabetes mellitus therapeutic target. The molecular interactions between the inhibitory peptides and the active site of DPP-IV have not been thoroughly examined, nor have their pharmacokinetic properties. Therefore, the predictions of legumin- and provicilin-derived DPP-IV inhibitory peptides, their molecular interactions with the active site of DPP-IV, and their pharmacokinetic properties were carried out. Ninety-two unique DPP-IV inhibitory peptides were identified. Papain and trypsin were the enzymes with the highest AE (0.0927) and lowest BE (6.8625 × 10-7) values, respectively. Peptide binding energy values ranged from -5.2 to -7.9 kcal/mol. HIS-PHE was the most potent DPP-IV inhibitory peptide and interacts with residues of the active sites S1 (TYR662) and S2 (GLU205/ARG125 (hydrogen bonds: <3.0 Å)), S2 (GLU205/GLU206 (electrostatic interactions: <3.0 Å)), and S2' pocket (PHE357 (hydrophobic interaction: 4.36 Å)). Most peptides showed optimal absorption (76.09%), bioavailability (89.13%), and were non-toxic (97.8%) stable for gastrointestinal digestion (73.9%). Some peptides (60.86%) could also inhibit ACE-I. Chickpea is a source of non-toxic and bioavailable DPP-IV-inhibitory peptides with dual bioactivity. Studies addressing the potential of chickpea peptides as therapeutic or adjunct agents for treating type 2 diabetes are warranted.

Preparation of quinoa protein with ultrasound pretreatment and its effects on the physicochemical properties, structural and digestion characterizations

This study aimed to investigate the effects of ultrasound pretreatment on the yield and the physicochemical properties, structural and digestion characterizations of quinoa protein (QP). Results showed that under the conditions of ultrasonic power density of 0.64 W/mL, ultrasonication time of 33 min, and the liquid-solid ratio of 24 mL/g, the highest yield of QP at 68.403 % was obtained, which was significantly higher than that without ultrasound pretreatment at 51.26 ± 1.76 % (P < 0.05). Ultrasound pretreatment decreased the average particle size and ζ-potential but increased the hydrophobicity of QP (P < 0.05). However, no significant protein degradation and secondary structure changes of QP by ultrasound pretreatment were observed. In addition, ultrasound pretreatment slightly improved the in vitro digestibility of QP and reduced the dipeptidyl peptidase IV (DPP-IV) inhibitory activity of the hydrolysate of QP by in vitro digestion. Overall, this work demonstrates that ultrasound-assisted extraction is appropriate for improving the extraction efficiency of QP.

Narrative Review on the Effects of Oat and Sprouted Oat Components on Blood Pressure

Hypertension (HTN) is a major risk factor for cardiovascular disease (CVD) and cognitive decline. Elevations in blood pressure (BP) leading to HTN can be found in young adults with increased prevalence as people age. Oats are known to decrease CVD risk via an established effect of β-glucan on the attenuation of blood cholesterol. Many past studies on CVD and oats have also reported a decrease in BP; however, a thorough assessment of oats and BP has not been conducted. Moreover, oats deliver several beneficial dietary components with putative beneficial effects on BP or endothelial function, such as β-glucan, γ-amino butyric acid (GABA), and phytochemicals such as avenanthramides. We conducted a comprehensive search for systematic reviews, meta-analyses, and clinical intervention studies on oats and BP and identified 18 randomized controlled trials (RCTs) and three meta-analyses that supported the role of oats in decreasing BP. Emerging data also suggest oat consumption may reduce the use of anti-hypertensive medications. The majority of these studies utilized whole oats or oat bran, which include a vast array of oat bioactives. Therefore, we also extensively reviewed the literature on these bioactives and their putative effect on BP-relevant mechanisms. The data suggest several oat components, such as GABA, as well as the delivery of high-quality plant protein and fermentable prebiotic fiber, may contribute to the anti-HTN effect of oats. In particular, GABA is enhanced in oat sprouts, which suggests this food may be particularly beneficial for healthy BP management.

Preparation and Characterization of an Anticancer Peptide from Oriental Tonic Food Enteromorpha prolifera

Enteromorpha prolifera (E. prolifera), a tonic food in East Asian countries, is frequently studied for their pharmaceutical and healthcare applications. However, limited research has focused on antitumor peptides derived from this edible seaweed. In this study, we aimed to investigate the anticancer properties of peptides isolated from the hydrolysate of E. prolifera generated by a plethora of proteases including trypsin, papain, bromelain, and alkaline protease. The results showed that the hydrolysate produced by papain digestion exhibited remarkably stronger anticancer activity and was subjected to further purification by ultrafiltration and sequential chromatography. One heptapeptide, designated HTDT-6-2-3-2, showed significant antiproliferation activity towards several human cancer cell lines. The IC50 values for NCI-H460, HepG2, and A549 were 0.3686 ± 0.0935 mg/mL, 1.2564 ± 0.0548 mg/mL, and 0.9867 ± 0.0857 mg/mL, respectively. Moreover, results from flow cytometry confirmed that cell apoptosis was induced by HTDT-6-2-3-2 in a dose-dependent manner. The amino acid sequence for this heptapeptide, GPLGAGP, was characterized by Edman degradation and further verified by Liquid Chromatography-Tandem Mass Spectrometry. In silico analysis results suggested that XIAP could be a potential target for HTDT-6-2-3-2. Molecular docking simulation showed that HTDT-6-2-3-2 could occupy a shallow pocket in the BIR3 domain of XIAP, which is involved in the inhibitory effect of caspase-9 activation. In conclusion, this E. prolifera derived peptide exhibited strong anticancer properties, which could be explored for pharmaceutical applications.