Tryptophan-containing milk protein-derived dipeptides inhibit xanthine oxidase

Food-derived bioactive peptides with anti-hyperuricemic activity: A comprehensive review

Hyperuricemia (HU) is a metabolic disorder caused by the overproduction or underexcretion of uric acid (UA) in the human body. Several approved drugs for the treatment of HU are available in the market; however, all these allopathic drugs exhibit multiple side effects. Therefore, the development of safe and effective anti-HU drugs is an urgent need. Natural compounds derived from foods and plants have the potential to decrease UA levels. Recently, food-derived bioactive peptides (FBPs) have gained attention as a functional ingredient owing to their biological activities. In the current review, we aim to explore the urate-lowering potential and the underlying mechanisms of FBPs. We found that FBPs mitigate HU by reducing blood UA levels through inhibiting key enzymes such as xanthine oxidase, increasing renal UA excretion, inhibiting renal UA reabsorption, increasing anti-oxidant activities, regulating inflammatory mediators, and addressing gut microbiota dysbiosis. In conclusion, FBPs exhibit strong potential to ameliorate HU.

Camel whey protein with enhanced antioxidative and antimicrobial properties upon simulated gastro-intestinal digestion

Background: Whey proteins and their peptide derivatives have attracted a great attention of researchers in the pharmaceutical and nutritional fields, due to their numerous bio-functionalities. Aim: In the present research study, enzymatic protein hydrolysates (CWPHs) from camel whey proteins (CWPs) were produced and investigated for their antioxidant and antimicrobial potentials. Methods: Herein, Pepsin (gastric), and Trypsin and Chymotrypsin (pancreatic) enzymes were used to produce CWPHs. The obtained hydrolysates were characterize to ascertain the level of protein degradation and studies on their antimicrobial and antioxidant potential were conducted. Results: Among all CWPHs, a complete degradation of all different protein bands was perceived with Chymotrypsin-derived CWPHs, whereas, light bands of serum albumin and α-lactalbumin were observed with Trypsin and Pepsin-derived CWPHs. After enzymatic degradation, both CWPHs antioxidant and antimicrobial activities were improved. Chymotrypsin-derived CWPHs demonstrated higher DPPH and ABTS radical scavenging activities, anent the increase in proteolysis time. Compared to unhydrolyzed CWPs, higher metal chelating activities were displayed by Trypsin-derived CWPHs. No significant increase in the FRAP activities was noticed after CWPs hydrolysis using Trypsin and Chymotrypsin, while Pepsin-derived CWPHs showed higher reducing power. In terms of antimicrobial activity, significantly higher bacterial growth inhibition rates were exhibited by CWPHs compared to the unhydrolyzed CWP. Conclusion: Overall, CWPHs displayed enhanced antioxidative and antimicrobial properties.

A strategy to boost xanthine oxidase and angiotensin converting enzyme inhibitory activities of peptides via molecular docking and module substitution

Molecular docking and activity evaluation screened the dipeptide module GP with low xanthine oxidase (XOD) inhibitory activity and modules KE and KN with high activity, and identified them as low- and high-contribution modules, respectively. We hypothesized the substitution of low-contribution modules in peptides with high contributions would boost their XOD inhibitory activity. In the XOD inhibitory peptide GPAGPR, substitution of GP with both KE and KN led to enhanced affinity between the peptides and XOD. They also increased XOD inhibitory activity (26.4% and 10.3%) and decreased cellular uric acid concentrations (28.0% and 10.4%). RNA sequencing indicated that these improvements were attributable to the inhibition of uric acid biosynthesis. In addition, module substitution increased the angiotensin-converting enzyme inhibitory activity of GILRP and GAAGGAF by 84.8% and 76.5%. This study revealed that module substitution is a feasible strategy to boost peptide activity, and provided information for the optimization of hydrolysate preparation conditions.

Antihyperuricemic activity and inhibition mechanism of xanthine oxidase inhibitory peptides derived from whey protein by virtual screening

Xanthine oxidase (XO), a rate-limiting enzyme in uric acid production, is the pivotal therapeutic target for gout and hyperuricemia. In this study, 57 peptides from α-lactalbumin and β-lactoglobulin were obtained via virtual enzymatic hydrolysis, and 10 XO inhibitory peptides were virtually screened using molecular docking. Then toxicity, allergenicity, solubility, and isoelectric point of the obtained 10 novel peptides were evaluated by in silico tools. The XO activity of these synthetic peptides was tested using an in vitro assay by high-performance liquid chromatography. Their inhibitory mechanism was further explored by molecular docking. The results showed that 4 peptides GL, PM, AL, and AM exhibited higher inhibitory activity, and their half maximal inhibitory concentration in vitro was 10.20 ± 0.89, 23.82 ± 0.94, 34.49 ± 0.89, and 40.45 ± 0.92 mM, respectively. The peptides fitted well with XO through hydrogen bond, hydrophobic interaction, and van der Waals forces, and amino acid residues Glu802, Leu873, Arg880, and Pro1076 played an important role in this process. Overall, this study indicated 4 novel peptides GL, PM, AL, and AM from whey protein exhibited XO inhibitory activity, and they might be useful and safe XO inhibitors for hyperuricemia prevention and treatment.

Virtual screening and structure optimization of xanthine oxidase inhibitory peptides from whole protein sequences of Pacific white shrimp via molecular docking

Xanthine oxidase (XO) inhibitory peptides are safer than conventional pharmacological therapy in relieving hyperuricemia. However, traditional enzymatic hydrolysis, separation, and purification techniques for bio-active peptide preparation are time-consuming, inefficient, and labor-intensive. In this study, molecular docking and BLAST were used to virtually screen XO inhibitory peptides from whole protein sequences of Pacific white shrimp according to the bio-active peptides database, and the structure of peptides was optimized based on the structure-effective relationship. Seven new XO inhibitory peptides were virtual screened rapidly from Pacific white shrimp, and YNITGW (IC50 = 9.78 ± 0.13 mM) showed the strongest activity. The results of YNITGW optimization showed that the insertion of Trp residue in the middle position of peptides could effectively enhance the activity. This study revealed that screening and optimizing peptides by molecular docking were a novel and feasible method to obtain bio-active peptides.

Understanding Hyperuricemia: Pathogenesis, Potential Therapeutic Role of Bioactive Peptides, and Assessing Bioactive Peptide Advantages and Challenges

Hyperuricemia is a medical condition characterized by an elevated level of serum uric acid, closely associated with other metabolic disorders, and its global incidence rate is increasing. Increased synthesis or decreased excretion of uric acid can lead to hyperuricemia. Protein peptides from various food sources have demonstrated potential in treating hyperuricemia, including marine organisms, ovalbumin, milk, nuts, rice, legumes, mushrooms, and protein-rich processing by-products. Through in vitro experiments and the establishment of cell or animal models, it has been proven that these peptides exhibit anti-hyperuricemia biological activities by inhibiting xanthine oxidase activity, downregulating key enzymes in purine metabolism, regulating the expression level of uric acid transporters, and restoring the composition of the intestinal flora. Protein peptides derived from food offer advantages such as a wide range of sources, significant therapeutic benefits, and minimal adverse effects. However, they also face challenges in terms of commercialization. The findings of this review contribute to a better understanding of hyperuricemia and peptides with hyperuricemia-alleviating activity. Furthermore, they provide a theoretical reference for developing new functional foods suitable for individuals with hyperuricemia.

Potential of milk-derived bioactive peptides as antidiabetic, antihypertensive, and xanthine oxidase inhibitors: a comprehensive bibliometric analysis and updated review

Bioactive peptides consist of small protein fragments, which are inactive in their original conformation, and they become active when released from these through enzymatic hydrolysis or fermentation processes. The bioactivity of such peptides has been extensively reported in the literature as contributors to organic homeostasis processes, as well as in immunomodulation, organism defense against oxidative processes, among others. In this study, reports of the activity of BPs isolated from milk with the potential glycemic control, antihypertensive activity, and inhibitors of uric acid formation were compiled. A systematic literature review and bibliometric analysis were conducted, using the PICO strategy for the research. The temporal analysis of publications revealed a growing interest in the investigation of bioactive peptides with potential antidiabetic, antihypertensive, and xanthine oxidase inhibitory activities, using dairy sources as products for their extraction. The literature analysis also revealed an increase in research involving non-bovine dairy products for bioactive peptide extraction. The collaboration network among authors exhibited weaknesses in scientific cooperation. Regarding the analysis of keywords, the usage of terms such as "bioactive peptides", "antioxidant", "antihypertensive", and "diabetes" was evident, constituting the main research clusters. Peptides with low molecular weight, typically < 10 kDa, of hydrophobic nature with aliphatic and aromatic chains, have significant implications in molecular interactions for the required activities. Although there is a growing interest in the industry regarding the utilization of bioactive peptides as potential drugs, there is a need to address gaps related to elucidating their interactions with cellular targets and their use in human therapy.

Walnut Protein: A Rising Source of High-Quality Protein and Its Updated Comprehensive Review

Recently, plant protein as a necessary nutrient source for human beings, a common ingredient of traditional processed food, and an important element of new functional food has gained prominence due to the increasing demand for healthy food. Walnut protein (WP) is obtained from walnut kernels and walnut oil-pressing waste and has better nutritional, functional, and essential amino acids in comparison with other vegetable and grain proteins. WP can be conveniently obtained by various extraction techniques, including alkali-soluble acid precipitation, salting-out, and ultrasonic-assisted extraction, among others. The functional properties of WP can be modified for desired purposes by using some novel methods, including free radical oxidation, enzymatic modification, high hydrostatic pressure, etc. Moreover, walnut peptides play an important biological role both in vitro and in vivo. The main activities of the walnut peptides are antihypertensive, antioxidant, learning improvement, and anticancer, among others. Furthermore, WP could be applied in the development of functional foods or dietary supplements, such as delivery systems and food additives, among others. This review summarizes recent knowledge on the nutritional, functional, and bioactive peptide aspects of WP and possible future products, providing a theoretical reference for the utilization and development of oil crop waste.

Purification and identification of xanthine oxidase inhibitory peptides from enzymatic hydrolysate of α-lactalbumin and bovine colostrum casein

The development of food-derived Xanthine Oxidase (XO) inhibitors is critical to the treatment of hyperuricemia and oxidative stress-related disease. Few studies report on milk protein hydrolysates' XO inhibitory activity, with the mechanism of their interaction remaining elusive. Here, different commercial enzymes were used to hydrolyze α-lactalbumin and bovine colostrum casein. The two proteins hydrolyzed by alkaline protease exhibited the most potent XO inhibitory activity (bovine casein: IC₅₀ = 0.13 mg mL^-1; α-lactalbumin: IC₅₀ = 0.28 mg mL^-1). Eight potential XO inhibitory peptides including VYPFPGPI, GPVRGPFPIIV, VYPFPGPIPN, VYPFPGPIHN, QLKRFSFRSFIWR, LVYPFPGPIHN, AVFPSIVGR, and GFININSLR (IC₅₀ of 4.67-8.02 mM) were purified and identified from alkaline protease hydrolysates by using gel filtration, LC-MS/MS and PeptideRanker. The most important role of inhibiting activity of peptides is linked to hydrophobic interactions and hydrogen bonding based on the results of molecular docking and molecular dynamics simulation. The enzymatic hydrolysate of α-lactalbumin and bovine colostrum casein could be a competitive candidates for hyperuricemia-resisting functional food.

Releasing Bioactive Compounds from Brown Seaweed with Novel Cold-Adapted Alginate Lyase and Alcalase

Seaweeds are considered to be third-generation renewable biomasses, the comprehensive utilization of which has drawn increasing attention in recent years. A novel cold-active alginate lyase (VfAly7) was identified from Vibrio fortis and biochemically characterized for brown seaweed utilization. The alginate lyase gene was high-level expressed in Pichia pastoris, with an enzyme yield of 560 U/mL and a protein content of 9.8 mg/mL by high-cell density fermentation. The recombinant enzyme was most active at 30 °C and pH 7.5, respectively. VfAly7 was a bifunctional alginate lyase with both poly-guluronate and poly-mannuronate hydrolysis activities. On the basis of VfAly7, a bioconversion strategy for the utilization of brown seaweed (Undaria pinnatifida) was developed. The obtained AOSs showed stronger prebiotic activity towards tested probiotics when compared to that of commercial fructooligosaccharides (FOSs), while the obtained protein hydrolysates displayed strong xanthine oxidase inhibitory activity with IC50 of 3.3 mg/mL. This study provided a novel alginate lyase tool as well as a biotransformation route for the utilization of seaweeds.

Xanthine Oxidase Inhibitory Peptides from Larimichthys polyactis: Characterization and In Vitro/In Silico Evidence

Hyperuricemia is linked to a variety of disorders that can have serious consequences for human health. Peptides that inhibit xanthine oxidase (XO) are expected to be a safe and effective functional ingredient for the treatment or relief of hyperuricemia. The goal of this study was to discover whether papain small yellow croaker hydrolysates (SYCHs) have potent xanthine oxidase inhibitory (XOI) activity. The results showed that compared to the XOI activity of SYCHs (IC₅₀ = 33.40 ± 0.26 mg/mL), peptides with a molecular weight (MW) of less than 3 kDa (UF-3) after ultrafiltration (UF) had stronger XOI activity, which was reduced to IC₅₀ = 25.87 ± 0.16 mg/mL (p < 0.05). Two peptides were identified from UF-3 using nano-high-performance liquid chromatography-tandem mass spectrometry. These two peptides were chemically synthesized and tested for XOI activity in vitro. Trp-Asp-Asp-Met-Glu-Lys-Ile-Trp (WDDMEKIW) (p < 0.05) had the stronger XOI activity (IC₅₀ = 3.16 ± 0.03 mM). The XOI activity IC₅₀ of the other peptide, Ala-Pro-Pro-Glu-Arg-Lys-Tyr-Ser-Val-Trp (APPERKYSVW), was 5.86 ± 0.02 mM. According to amino acid sequence results, the peptides contained at least 50% hydrophobic amino acids, which might be responsible for reducing xanthine oxidase (XO) catalytic activity. Furthermore, the inhibition of the peptides (WDDMEKIW and APPERKYSVW) against XO may depend on their binding to the XO active site. According to molecular docking, certain peptides made from small yellow croaker proteins were able to bind to the XO active site through hydrogen bonds and hydrophobic interactions. The results of this work illuminate SYCHs as a promising functional candidate for the prevention of hyperuricemia.

Multifunctional bioactive properties of hydrolysates from colocynth (Citrullus colocynthis) seeds derived proteins: Characterization and biological properties

Citrullus colocynthis (Colocynth) has gained a great deal of interest in their applications as indigenous nutraceutical and as a functional food ingredient. The intact colocynth seed protein was enzymatically hydrolyzed using proteolytic enzymes (alcalase, bromelain, and chymotrypsin) at different time intervals of 3, 6, and 9 h. The highest degree of hydrolysis (87.82%) was observed in chymotrypsin derived colocynth seed protein hydrolysates (CSPH) for 9 h. The CSPHs was further investigated through in-vitro assay to explore its potential biological activity such as antioxidant, inhibition of enzymatic marker related to diabetes (DPP-IV, α-glucosidase and α-amylase) and hyperlipidaemia (cholesteryl esterase and pancreatic lipase). Chymotrypsin hydrolysate showed the strongest DPPH (65.7 mM TEAC) and ABTS (525.2 mM TEAC) radical scavenging activity after 6 h of hydrolysis. Moreover, chymotrypsin-treated CSPH for 6 h inhibited cholesteryl esterase (IC₅₀ = 13.68 μg/mL) and pancreatic lipase (IC₅₀ = 14.12 μg/mL) significantly when compared to native protein. Whereas, bromelain and alcalase treated hydrolysate for 6 h effectively inhibited α-glucosidase and α-amylase at an inhibitory concentration of IC₅₀ = 13.27 μg/mL and of IC₅₀ = 17 μg/mL. Overall, the findings indicated that protein hydrolysates exhibited superior biological activity than intact colocynth seed proteins isolate (CSPI) and could be a sustainable source of bioactive peptides.

A modified xanthine oxidase cell model for screening of antihyperuricemic functional compounds

Hyperuricemia is a purine metabolism disorder, with increasing prevalence worldwide. Here, a high throughput cell model for screening of antihyperuricemic compounds was set up. Human kidney cells (HK2 cells) were stimulated with adenosine and the resulting supernatant and lysate were then analyzed using high performance liquid chromatography (HPLC). The results showed that hypoxanthine content was increased in both HK2 cells supernatant and xanthine oxidase (XO)-overexpressing HK2 cells lysate, but no uric acid was detected due to lower endogenous XO content in these cells. Exogenous XO was added to the supernatant, and then used to evaluate the antihyperuricemic activity of Febuxostat and two the previously identified peptides, Pro-Gly-Ala-Cys-Ser-Asn (PGACSN) and Trp-Met-Leu (WML). By adding exogenous XO, this combined-adenosine-XO-induced hyperuricemia model was optimized and established, and the Febuxostat and peptides were confirmed to significantly reduce uric acid production in the HK2 cells supernatant (p < 0.05). Therefore, this cell model could be recommended for screening potential bioactive antihyperuricemic compounds.

Novel xanthine oxidase inhibitory peptides derived from whey protein: identification, in vitro inhibition mechanism and in vivo activity validation

As the development of hyperuricemia (HUA) and gout continues to accelerate worldwide, there is increasing interest in the use of xanthine oxidase (XO) inhibitors as therapeutic agents for the management of HUA and gout. In the present study, XO inhibitory peptides were identified from whey protein isolate (WPI) hydrolysates, and the underlying inhibitory mechanism and in vivo activities was investigated. WPI hydrolysates were isolated and purified, and two peptides (ALPM and LWM) with lower binding energy were screened by molecular docking. The result showed that these two peptides interacted with residues around the active site of XO through hydrogen bond and hydrophobic interaction. The IC₅₀ values of ALPM and LWM were 7.23 ± 0.22 and 5.01 ± 0.31 mM, respectively. According to the Lineweaver-Burk curve, the inhibition types of ALPM and LWM were non-competitive inhibition. Circular dichroism (CD) spectra indicated ALPM and LWM could change the secondary structure of XO. Molecular dynamics simulations revealed that XO-peptide complexes were more stable and compact than XO. Moreover, animal studies have shown that ALPM and LWM have anti-hyperuricemia effects in vivo. This study suggested that ALPM and LWM can be considered as natural XO inhibitors for the treatment of HUA.

Novel anti-hyperuricemic hexapeptides derived from Apostichopus japonicus hydrolysate and their modulation effects on the gut microbiota and host microRNA profile

Hyperuricemia (HUA) is the second most common metabolic disease nowadays, and is characterized by permanently increased concentrations of serum uric acid. In this study, two novel hexapeptides (GPAGPR and GPSGRP) were identified from Apostichopus japonicus hydrolysate and predicted to have xanthine oxidase (XOD) inhibitory activity by molecular docking. Their in vitro XOD inhibition rates reached 37.3% and 48.6%, respectively, at a concentration of 40 mg mL^-1. Subsequently, in vivo experiments were carried out in a HUA mouse model, and we found that both peptides reduced the serum uric acid by inhibiting uric acid biosynthesis and reabsorption, as well as alleviated renal inflammation via suppressing the activation of the NLRP3 inflammasome. 16S rDNA sequencing indicated that both peptide treatments reduced the richness and diversity of the gut microbiota, altered the composition in the phylum and genus levels, but different change trends were observed in the phylum Verrucomicrobia and genera Akkermansia, Dubosiella, Alloprevotella, Clostridium unclassified and Alistipes. In addition, changes in the renal microRNA (miRNA) profiles induced by GPSGRP treatment were analyzed; 21 differentially expressed (DE) miRNAs were identified among groups, and KEGG pathway analysis indicated that their potential target genes were involved in pluripotency of stem cell regulation, mTOR signaling pathway and proteoglycans. Moreover, ten miRNAs involved in the HUA onset and alleviation were identified, which showed a high correlation with genera related to the metabolism of short-chain fatty acids, bile acids and tryptophan. This study delineated two hexapeptides as potential microbiota modulators and miRNA regulators that can ameliorate HUA.

Impact of Enzymatic Hydrolysis and Heat Inactivation on the Physicochemical Properties of Milk Protein Hydrolysates

This study determined the physicochemical properties (apparent viscosity (ηapp), turbidity (A550nm), particle size and molecular mass distribution) of hydrolysates generated from whey protein concentrate (WPC), milk protein concentrate (MPC) and sodium caseinate (NaCN), following incubation with Debitrase HYW20™ and Prolyve™ at 50 °C, pH 7.0 for 1 and 4 h, before and after heat inactivation (80 °C for 10 min). The degree of hydrolysis (DH) increased with incubation time, giving values of 6.56%, 8.17% and 9.48%, following 1 h hydrolysis of WPC, MPC and NaCN with Debitrase HYW20™, and 12.04%, 15.74% and 17.78%, respectively, following 4 h incubation. These DHs were significantly higher compared to those obtained following 4 h incubation with Prolyve™. Hydrolysis with Debitrase HYW20™ gave >40% of peptides with molecular masses < 1 kDa for all substrates, which was higher than the value obtained following hydrolysis with Prolyve™. The effect of hydrolysis on the physicochemical properties was substrate dependent, since ηapp decreased in WPC and NaCN hydrolysates, particle size decreased for all the substrates, with aggregate formation for MPC, and turbidity decreased in WPC and MPC hydrolysates, while it increased in NaCN hydrolysates. The physical properties of the hydrolysates were influenced by the enzyme thermal inactivation step in a DH-dependent manner, with no significant effect on turbidity and viscosity for hydrolysates at higher DHs.

Identification and characterization of cholesterol esterase and lipase inhibitory peptides from amaranth protein hydrolysates

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Gastric, microbial and plant-based enzymes were used to produce Amaranth protein hydrolysates (APHs).

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APHs displayed enhanced cholesterol esterase (CEase) and pancreatic lipase (PL) inhibitory activities.

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Bromelain generated hydrolysates showed the highest CEase and PL inhibitory activity.

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FPFPPTLGY, FGAPR, and FPFVPAPT were predicted as potential PL inhibitors and FPFVPAPT as CEase inhibitor.

Human diet is undergoing a shift towards plant-based diet as a sustainable source of protein compared to animal-derived protein. In this study, cholesterol esterase (CEase) and pancreatic lipase (PL) inhibitory activities of amaranth protein hydrolysates (APHs) were studied. Bromelain, chymotrypsin, and actinase E were used for generating APHs at 2, 4 & 6 h of hydrolysis. Higher PL inhibiting potential were observed in bromelain-derived APHs (IC₅₀ = 0.38–0.66 mg/mL) in comparison to intact amaranth proteins (IC₅₀ = 3.93 mg/mL). Bromelain-4 h hydrolysates (AB4) demonstrated significant inhibitory potential for both CEase (IC₅₀ = 0.47 mg/mL) and PL (IC₅₀ = 0.48 mg/mL) activity. Peptide identification in AB-4 hydrolysate revealed that among 17 bioactive peptides, three peptides (FPFPPTLGY, FGAPR, and FPFVPAPT) were predicted as potential PL inhibitors and only one peptide (FPFVPAPT) was predicted as CEase inhibitor based on the number of substrate binding sites on active site of the enzymes. This is the first study providing insights into amaranth protein derived bioactive peptide possessing CEase and LIP inhibitory potential.

Systematic investigation of the amino acid profiles that are correlated with xanthine oxidase inhibitory activity: Effects, mechanism and applications in protein source screening

This study aimed to investigate the dipeptide amino acid profiles correlated with xanthine oxidase (XOD) inhibitory activity and guide screening to determine suitable sources for XOD inhibitor protein hydrolysate preparation. The XOD inhibitory activities of 400 dipeptides were predicted via molecular docking and measured in vitro, and amino acids containing aromatic structures and charged residues were correlated with high XOD inhibitory properties. Subsequently, the effects of Cys-Glu and Lys-Glu, which showed the highest in vitro activities, were examined in hyperuricaemic mice, and were found to alleviate hyperuricaemia and modulate the gut microbiota. Furthermore, a suitable protein from Oreochromis mossambicus with high contents of charged (8.6%) and aromatic (1.67%) amino acids was screened, and the in vitro inhibitory rates of protein hydrolysate prepared from O. mossambicus against XOD were found to be 21.90% and 44.51% at 40 and 100 mg/ml, respectively. This study provides a strategy for screening protein hydrolysate sources with certain activities based on amino acid profiles.

Hypouricemic, hepatoprotective and nephroprotective roles of oligopeptides derived from Auxis thazard protein in hyperuricemic mice

The oligopeptides derived from Auxis thazard protein (ATO) are a class of small peptides with molecular weight <1 kDa and good bioactivity. This paper aimed to explore the hypouricemic, hepatoprotective, and nephroprotective effects of ATO and its potential mechanisms in hyperuricemia in mice induced by potassium oxonate. The results showed that ATO significantly reduced serum UA, serum creatinine levels, inhibited XOD and ADA activities in the liver (p < 0.05), and accelerated UA excretion by downregulating the gene expression of renal mURAT1 and mGLUT9 and upregulating the gene expression of mABCG2 and mOAT1. ATO could also reduce the levels of liver MDA, increase the activities of SOD and CAT, and reduce the levels of IL-1β, MCP-1 and TNF-α. Histological analysis also showed that ATO possessed hepatoprotective and nephroprotective activities in hyperuricemic mice. Thus, ATO could reduce the serum UA level in hyperuricemic mice by decreasing UA production and promoting UA excretion from the kidney, suggesting that ATO could be developed as a dietary supplement for hyperuricemia treatment.

Purification and Identification of Novel Xanthine Oxidase Inhibitory Peptides Derived from Round Scad (Decapterus maruadsi) Protein Hydrolysates

The objective of the present study was to investigate the xanthine oxidase (XO) inhibitory effects of peptides purified and identified from round scad (Decapterus maruadsi) hydrolysates (RSHs). In this study, RSHs were obtained by using three proteases (neutrase, protamex and alcalase). Among them, the RSHs of 6-h hydrolysis by neutrase displayed the strongest XO inhibitory activity and had an abundance of small peptides (<500 Da). Four novel peptides were purified by immobilized metal affinity chromatography and identified by nano-high-performance liquid chromatography mass/mass spectrometry. Their amino acid sequences were KGFP (447.53 Da), FPSV (448.51 Da), FPFP (506.59 Da) and WPDGR (629.66 Da), respectively. Then the peptides were synthesized to evaluate their XO inhibitory activity. The results indicated that the peptides of both FPSV (5 mM) and FPFP (5 mM) exhibited higher XO inhibitory activity (22.61 ± 1.81% and 20.09 ± 2.41% respectively). Fluorescence spectra assay demonstrated that the fluorescence quenching mechanism of XO by these inhibitors (FPSV and FPFP) was a static quenching procedure. The study of inhibition kinetics suggested that the inhibition of both FPSV and FPFP was reversible, and the type of their inhibition was a mixed one. Molecular docking revealed the importance of π-π stacking between Phe residue (contained in peptides) and Phe⁹¹⁴ (contained in the XO) in the XO inhibitory activity of the peptides.

Anti-hyperuricemic and nephroprotective effects of whey protein hydrolysate in potassium oxonate induced hyperuricemic rats

BACKGROUND

Hyperuricemia (HUA) is a serious public health concern globally that needs to be solved. It is closely related to gout and other metabolic diseases. To develop a safe and effective dietary supplementation for alleviating HUA, we investigated the effects of whey protein hydrolysate (WPH) on HUA and associated renal dysfunction and explored their underlying mechanism.

RESULTS

Potassium oxonate was used to induce HUA in model rats, who were then administered WPH for 21 days. The results showed that WPH significantly inhibited xanthine oxidase and adenosine deaminase activity in serum and liver, decreased uric acid (UA), creatinine, and blood urea nitrogen levels in serum, and increased the UA excretion in urine. In addition, WPH downregulated the expression of urate transporter 1 and upregulated the expression of organic anion transporter 1, adenosine triphosphate binding cassette subfamily G member 2, organic cation/carnitine transporters 1 and 2, and organic cation transporter 1 in kidneys.

CONCLUSION

These findings demonstrated for the first time that WPH could alleviate HUA by inhibiting UA production and promoting UA excretion, and improve the renal dysfunction caused by HUA. Thus, WPH may be a potential functional ingredient for the prevention and treatment of HUA and associated renal dysfunction. © 2021 Society of Chemical Industry.

A comparative investigation into novel cholesterol esterase and pancreatic lipase inhibitory peptides from cow and camel casein hydrolysates generated upon enzymatic hydrolysis and in-vitro digestion

Cow (CwC) and camel casein (CaC) hydrolysates were generated using Alcalase™ (CwCA and CaCA) and Pronase-E (CwCP and CaCP) each for 3 and 6 h, and investigated for their potential to inhibit key lipid digesting enzymes i.e., pancreatic lipase (PL) and cholesteryl esterase (CE). Results revealed stronger PL and CE inhibition by CaC hydrolysates compared to CwC. Potent hydrolysates (CwCP-3 h and CaCA-6 h) upon simulated gastrointestinal digestion (SGID) showed significant improvement in inhibition of both PL and CE. However, both the SGID hydrolysates showed similar extent of PL and CE inhibition and were further sequenced for peptide identification. Peptides MMML, FDML, HLPGRG from CwC and AAGF, MSNYF, FLWPEYGAL from CaC hydrolysates were predicted to be most active PL inhibitory peptides. Peptide LP found in both CwC and CaC hydrolysates was predicted as active CE inhibitor. Thus, CwC and CaC could be potential source of peptides with promising CE and PL inhibitory properties.

New insights into the cholesterol esterase- and lipase-inhibiting potential of bioactive peptides from camel whey hydrolysates: Identification, characterization, and molecular interaction

Novel antihypercholesterolemic bioactive peptides (BAP) from peptic camel whey protein hydrolysates (CWPH) were generated at different time, temperature, and enzyme concentration (%). Hydrolysates showed higher pancreatic lipase- (PL; except 3 CWPH) and cholesterol esterase (CE)-inhibiting potential, as depicted by lower half-maximal inhibitory concentration values (IC₅₀ values) compared with nonhydrolyzed camel whey proteins (CWP). Peptide sequencing and in silico data depicted that most BAP from CWPH could bind active site of PL, whereas as only 3 peptides could bind the active site of CE. Based on higher number of reactive residues in the BAP and greater number of substrate binding sites, FCCLGPVPP was identified as a potential CE-inhibitory peptide, and PAGNFLPPVAAAPVM, MLPLMLPFTMGY, and LRFPL were identified as PL inhibitors. Molecular docking of selected peptides showed hydrophilic and hydrophobic interactions between peptides and target enzymes. Thus, peptides derived from CWPH warrant further investigation as potential candidates for adjunct therapy for hypercholesterolemia.

Food-Derived Bioactive Peptides with Antioxidative Capacity, Xanthine Oxidase and Tyrosinase Inhibitory Activity

Bioactive peptides (BPs) released by proteases from different food protein sources are often served as antioxidants in food applications. This study aims to investigate 11 BPs derived from fish and egg white as potential natural antioxidants by antioxidant activity assays. The kinetic activity of the BPs against xanthine oxidase (XOD) and tyrosinase was also analyzed. The antioxidative capacity of the BPs indicated that VWWW (VW4, mackerel meat), followed by IRW (IW3, egg white) and VKAGFAWTANQQLS (VS14, tuna backbone protein), possessed the highest antioxidant activity in 1,1-diphenyl-2-picrylhydrazyl radical (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) and reducing power (RP) assays. Both the free-radical scavenging score predicted from the AnOxPePred algorithm and the DPPH, ABTS and RP results indicated that VW4 was the best antioxidant. Furthermore, the XOD and tyrosinase inhibition by three selected peptides exhibited competitive patterns of effective inhibition. The half maximal inhibitory concentrations (IC50) of the peptides for XOD inhibition were 5.310, 3.935, and 1.804 mM for VW4, IW3, and VS14, respectively, and they could serve as competitive natural XOD inhibitors. The IC50 of the peptides for tyrosinase inhibition were 1.254, 2.895, and 0.595 mM for VW4, IW3, and VS14, respectively. Overall, VW4, IW3, and VS14 are potential antioxidants and natural XOD inhibitors for preventing milk-fat oxidation, and anti-browning sources for inhibiting food-derived tyrosinase oxidation.

Camel whey protein hydrolysates induced G2/M cellcycle arrest in human colorectal carcinoma

Camel milk has been gaining immmense importance due to high nutritious value and medicinal properties. Peptides from milk proteins is gaining popularity in various therapeutics including human cancer. The study was aimed to investigate the anti-cancerous and anti-inflammatory properties of camel whey protein hydrolysates (CWPHs). CWPHs were generated at three temperatures (30 ℃, 37 ℃, and 45 ℃), two hydrolysis timepoints (120 and 360 min) and with three different enzyme concentrations (0.5, 1 and 2 %). CWPHs demonstrated an increase in anti-inflammatory effect between 732.50 (P-6.1) and 3779.16 (P-2.1) µg Dicolfenac Sodium Equivalent (DSE)/mg protein. CWPHs (P-4.3 & 5.2) inhibited growth of human colon carcinoma cells (HCT116) with an IC50 value of 231 and 221 μg/ml, respectively. P-4.3 induced G2/M cell cycle arrest and modulated the expression of Cdk1, p-Cdk1, Cyclin B1, p-histone H3, p21 and p53. Docking of two peptides (AHLEQVLLR and ALPNIDPPTVER) from CWPHs (P-4.3) identified Polo like kinase 1 as a potential target, which strongly supports our in vitro data and provides an encouraging insight into developing a novel peptide-based anticancer formulation. These results suggest that the active component, CWPHs (P-4.3), can be further studied and modeled to form a small molecule anti-cancerous therapy.

Simulated gastrointestinal digestion of camel and bovine casein hydrolysates: Identification and characterization of novel anti-diabetic bioactive peptides

Camel milk proteins are an important substrate for bioactive peptides generation. This study investigates in-vitro antidiabetic effect (via inhibition of α-amylase (AA), α-glucosidase (AG) and dipeptidyl peptidase IV (DPP-IV)) of bovine (BC) and camel casein (CC) hydrolysates. Further, effect of simulated gastrointestinal digestion (SGID) on inhibitory potential of generated hydrolysates was also explored. Both BC and CC hydrolysates displayed potent inhibitory properties against AA (IC₅₀ value- 0.58 & 0.59 mg/mL), AG (IC₅₀ value- 1.04 & 0.59 mg/mL) and DPP-IV (IC₅₀ value- 0.62 & 0.66 mg/mL), respectively. Among different peptides identified in BC and CC hydrolysates, it was observed that FLWPEYGAL was predicted to be most potent inhibitory peptide against AA. While LPTGWLM, MFE and GPAHCLL as most active inhibitor of AG and HLPGRG, QNVLPLH and PLMLP were predicted to be active against DPP-IV. Overall, BC and CC hydrolysates can be proposed to be used in different food formulations as functional antidiabetic agents.

Purification, identification, and computational analysis of xanthine oxidase inhibitory peptides from kidney bean

Hyperuricemia is related to plenty of diseases, seriously damaging human health. Current clinical drugs used to treat hyperuricemia have many adverse effects. In this study, kidney bean hydrolysate (KBH) was found to exert high xanthine oxidase inhibitory (XOI) activity. Compared to KBH (50.31 ± 2.73%), XOI activities of three fractions (M_w <5 kDa, M_w <3 kDa, M_w  < 1 kDa) by ultrafiltration were higher and increased to 58.58 ± 3.57%, 59.34 ± 1.78%, and 55.05 ± 5.00%, respectively (P < 0.05). A total of 69 peptides were identified by HPLC-ESI-MS/MS and analyzed binding affinities with XO with the help of molecular docking. AVDSLVPIGR, DWYDIK, LDNLLR, ISPIPVLK, ISSLEMTR showed well binding affinities with XO and DWYDIK presented the highest XOI activity (68.63 ± 5.07%) among five synthetic peptides (P < 0.05). Additionally, visual analysis results indicated that DWYDIK was pushed into the hydrophobic channel and formed hydrogen bonds with pivotal amino acids of xanthine oxidase. Overall, KBH could be a promising candidate as anti- hyperuricemia functional food. PRACTICAL APPLICATION: This research initially revealed that kidney bean peptides could significantly inhibit the activity of xanthine oxidase, indicating kidney bean peptides could be a treatment for hyperuricemia. Kidney bean peptides may have commercial potentials as a safer alternative with few side effects to drugs.

Exploring the potential of novel xanthine oxidase inhibitory peptide (ACECD) derived from Skipjack tuna hydrolysates using affinity-ultrafiltration coupled with HPLC-MALDI-TOF/TOF-MS

This study aimed to isolate and investigate the potential of the peptide alanine-cysteine-glutamic acid-cysteine-aspartic acid (ACECD), a novel xanthine oxidase inhibitory (XODI) peptide derived from Skipjack tuna hydrolysate (HS). Ultrafiltration membranes were used to obtain HS-based peptides as successive ultrafiltration fractions (of decreasing molecular weight) of UF-1, UF-2, UF-3, and UF-4. Their antioxidant and xanthine oxidase (XOD) inhibitory activities were determined and further characterized by affinity-ultrafiltration coupled with HPLC-MALDI-TOF/TOF-MS and in silico techniques. The results showed that peptides with a molecular weight (MW) cutoff of 600-1000 Da (UF-2) exhibited the highest antioxidant and XODI activities. A novel XODI peptide (ACECD) was identified with an IC₅₀ value of 13.40 mmol/L, which decreased by 21.24% and 51.40% compared to those of UF-2 and HS, respectively. Molecular docking indicated that ACECD inserted into the active center of Mo atoms in XOD, which led to competitive attachment with XOD and caused inhibition. The study findings indicated that the ACECD peptide could be useful as a safe XODI substance to alleviate hyperuricemia.

Discovery of a novel rice-derived peptide with significant anti-gout potency

As a metabolic disease, gout, which seriously affects the normal life of patients, has become increasingly common in modern society. However, the existing medicines cannot completely meet the clinical needs. In the current study, a novel short peptide (named rice-derived-peptide-2 (RDP2), AAAAGAMPK-NH2, 785.97 Da) was isolated and identified from water extract of shelled Oryza sativa fruits, without toxic side effects but excellent stability. Our results indicated that RDP2 (the minimum effective concentration is 5 μg kg^-1) induced a significant reduction in serum uric acid levels in hyperuricemic mice via suppressing xanthine oxidase activity and urate transporter 1 expression, as well as alleviated renal damage through inhibiting the activation of NLRP3 inflammasome. In addition, RDP2 can also alleviate paw swelling and inflammatory reactions in mice after subcutaneous injection of monosodium urate crystals. As mentioned above, we obtained a novel peptide which could work through all stages of gout, not only reducing uric acid levels and renal damage in hyperuricemic mice, but also alleviating inflammatory responses associated with acute gout attack, and thus provided a new peptide molecular template for the development of anti-gout drugs.

Molecular basis of the anti-diabetic properties of camel milk through profiling of its bioactive peptides on dipeptidyl peptidase IV (DPP-IV) and insulin receptor activity

The molecular basis of the anti-diabetic properties of camel milk reported in many studies and the exact active agent are still elusive. Recent studies have reported effects of camel whey proteins (CWP) and their hydrolysates (CWPH) on the activities of dipeptidyl peptidase IV (DPP-IV) and the human insulin receptor (hIR). In this study, CWPH were generated, screened for DPP-IV binding in silico and inhibitory activity in vitro, and processed for peptide identification. Furthermore, pharmacological action of intact CWP and their selected hydrolysates on hIR activity and signaling and on glucose uptake were investigated in cell lines. Results showed inhibition of DPP-IV by CWP and CWPH and their positive action on hIR activation and glucose uptake. Interestingly, the combination of CWP or CWPH with insulin revealed a positive allosteric modulation of hIR that was drastically reduced by the competitive hIR antagonist. Our data reveal for the first time the profiling and pharmacological actions of CWP and their derived peptides fractions on hIR and their pathways involved in glucose homeostasis. This sheds more light on the anti-diabetic properties of camel milk by providing the molecular basis for the potential use of camel milk in the management of diabetes.

RDP3, A Novel Antigout Peptide Derived from Water Extract of Rice

Gout and hyperuricemia can seriously affect the quality of life; at present, however, existing medicines are unable to meet all clinical needs. In the current study, a novel peptide (i.e., rice-derived-peptide-3 (RDP3), AAAAMAGPK-NH₂, 785.97 Da) in water extract obtained from shelled Oryza sativa fruits was identified. Testing revealed that RDP3 (minimum effective concentration 100 μg/kg) did not show both hemolytic and acute toxicity, and reduced uric acid levels in the serum of hyperuricemic mice by inhibiting xanthine oxidase activity and decreasing urate transporter 1 expression. RDP3 also alleviated renal injury in hyperuricemic mice by decreasing NLRP3 inflammasome expression. Furthermore, RDP3 alleviated formalin-induced paw pain and reduced monosodium urate crystal-induced paw swelling and inflammatory factors in mice. Thus, this newly identified peptide reduced uric acid levels and renal damage in hyperuricemic mice and showed anti-inflammatory and analgesic activities, indicating the potential of RDP3 as an antigout medicine candidate.

Tailoring the Adsorption of ACE-Inhibiting Peptides by Nitrogen Functionalization of Porous Carbons

Bioactive peptides, such as isoleucyl-tryptophan (IW), exhibit a high potential to inhibit the angiotensin-converting enzyme (ACE). Adsorption on carbon materials provides a beneficial method to extract these specific molecules from the complex mixture of an α-lactalbumin hydrolysate. This study focuses on the impact of nitrogen functionalization of porous carbon adsorbents, either via pre- or post-treatment, on the adsorption behavior of the ACE-inhibiting peptide IW and the essential amino acid tryptophan (W). The commercially activated carbon Norit ROX 0.8 is compared with pre- and postsynthetically functionalized N-doped carbon in terms of surface area, pore size, and surface functionality. For prefunctionalization, a covalent triazine framework was synthesized by trimerization of an aromatic nitrile under ionothermal conditions. For the postsynthetic approach, the activated carbon ROX 0.8 was functionalized with the nitrogen-rich molecule melamine. The batch adsorption results using model mixtures containing the single components IW and W could be transferred to a more complex mixture of an α-lactalbumin hydrolysate containing a huge number of various peptides. For this purpose, reverse-phase high-pressure liquid chromatography with fluorescence detection was used for identification and quantification. The treatment with the three different carbon materials leads to an increase in the ACE-inhibiting effect in vitro. The modified surface structure of the carbon via pre- or post-treatment allows separation of IW and W due to the certain selectivity for either the amino acid or the dipeptide.

Effects of heating or ultrasound treatment on the enzymolysis and the structure characterization of hempseed protein isolates

The effects of heating (90 °C/30 min) or ultrasound (200/400/600 W) treatment on antioxidant and angiotensin-converting enzyme inhibitory (ACEI) activity of hydrolysates from hempseed protein isolates (HPI) were studied. The secondary structure, surface hydrophobicity, intrinsic fluorescence, scanning electron microscopy (SEM) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of HPI treated by heating or ultrasound were measured. The results showed that hydrolysate from HPI treated with ultrasound at 200 W showed higher hydrolysis degree, proportion of lower molecular mass components (1.0-3.0 kDa), antioxidant and ACEI activity than those from heating or high-power treated. The changes in secondary structure, surface hydrophobicity and intrinsic fluorescence indicated the unfolding of HPI after ultrasound. The SEM results showed that HPI treated with ultrasound at 200 W exhibited decrease in particle size and deformation and further increased in power caused the aggregates of HPI. In conclusion, the ultrasound treatment at low-power was superior to 90 °C/30 min treatment in facilitating enzymatic release of antioxidant and ACEI peptides from HPI.

Novel xanthine oxidase-based cell model using HK-2 cell for screening antihyperuricemic functional compounds

Hyperuricemia is a metabolic disease caused by disorders of purine metabolism, the prevalence of which has increased worldwide. Here, a cell model for high uric acid production was established in vitro employing cultured human kidney cells (HK-2 cells), and its molecular basis was analyzed using gene expression profile. High performance liquid chromatography (HPLC) was used to monitor the content of metabolites in cell culture media. Adenosine addition was found to induce HK-2 cells to produce uric acid precursors (inosine and hypoxanthine). Furthermore, the cell model was verified by confirming the antihyperuricemic effect of the widely used antihyperuricemic drugs allopurinol, probenecid, and febuxostat, as well as reported bioactive peptides and amino acids, encompassing glutathione, tryptophan and carnosine, which significantly reduced uric acid production in the HK-2 cells (p < 0.05). RNA-Seq technology was used to perform a wide transcriptome analysis of the hyperuricemic cell model, and the results demonstrated that it has the potential to be used as a rapid and valid in vitro model to screen antihyperuricemic compounds that mimics in vivo cell growth patterns.

New Rice-Derived Short Peptide Potently Alleviated Hyperuricemia Induced by Potassium Oxonate in Rats

Gout that caused by hyperuricemia affects human health seriously and more efficient drugs are urgently required clinically. In this study, a novel peptide named RDP1 (AAAAGAKAR, 785.91 Da) was identified from the extract of shelled fruits of Oryza sativa. Our results demonstrated that RDP1 (the minimum effective concentration is 10 μg/kg) could significantly reduce the serum uric acid and creatinine and alleviate hyperuricemic nephropathy in rats by intragastric administration. RDP1 inhibited xanthine oxidase, which also was verified at the animal level. Results from molecular docking indicated that RDP1 can inhibit uric acid formation by occupying the binding site of xanthine oxidase to xanthine. Besides, RDP1 showed no toxicity on rats and was stable in several temperatures, demonstrating its advantages for transportation. This research was the first discovery of antihyperuricemic peptide from the shelled fruits of O. Sativa and provided a new candidate for the development of hypouricemic drugs.