Peptide IPPKKNQDKTE ameliorates insulin resistance in HepG2 cells via blocking ROS-mediated MAPK signaling

Production of Food-Derived Bioactive Peptides with Potential Application in the Management of Diabetes and Obesity: A Review

The prevalence of diabetes mellitus and obesity is increasing worldwide. Bioactive peptides are naturally present in foods or in food-derived proteins. Recent research has shown that these bioactive peptides have an array of possible health benefits in the management of diabetes and obesity. First, this review will summarize the top-down and bottom-up production methods of the bioactive peptides from different protein sources. Second, the digestibility, bioavailability, and metabolic fate of the bioactive peptides are discussed. Last, the present review will discuss and explore the mechanisms by which these bioactive peptides help against obesity and diabetes based on in vitro and in vivo studies. Although several clinical studies have demonstrated that bioactive peptides are beneficial in alleviating diabetes and obesity, more double-blind randomized controlled trials are needed in the future. This review has provided novel insights into the potential of food-derived bioactive peptides as functional foods or nutraceuticals to manage obesity and diabetes.

Protective Effect of Glycomacropeptide on the Inflammatory Response of U937 Macrophages

Macrophages play crucial roles in inflammation and oxidative stress associated with noncommunicable diseases, such as cardiovascular diseases, diabetes, and cancer. Glycomacropeptide (GMP) is a bioactive peptide derived from milk κ-casein that contains abundant sialic acid and has shown anti-inflammatory, antioxidative, anti-obesity, and anti-diabetic properties when is orally administered. The aim of this study was to evaluate the effect of GMP on the regulation of the inflammatory response in human macrophages and the participation of sialic acid in this activity. GMP pretreatment decreased by 35%, 35%, and 49% the production of nitrites, interleukin (IL)-1β, and tumor necrosis factor (TNF)-α, respectively, in activated human macrophages U937. The same effect was obtained when cells were pretreated with asialo GMP, and no change on the gene expression of the lectins associated with the recognition of sialic acids, SIGLEC5, 7, and 9, was induced by GMP on macrophages, which suggests that sialic acid might not be involved in this immunoregulatory effect. Interestingly, GMP increased 8.9- and 3.5-fold the gene expression of the canonical anti-inflammatory protein SOCS3 and the antioxidant enzyme HMOX1, respectively, in U937 cells. Thus, GMP exerts anti-inflammatory and antioxidative activities on activated macrophages in a sialic acid-independent manner, which might be related to its in vivo reported bioactivity.

Top-Down Glycopeptidomics Reveals Intact Glycomacropeptide Is Digested to a Wide Array of Peptides in Human Jejunum

BACKGROUND

Bovine milk κ-casein-derived caseinomacropeptide (CMP) is produced in large quantities during cheese-making and has various biological activities demonstrated via in vitro and in vivo experiments. Previous studies examined protein degradation and peptide release after casein or whey protein consumption. However, whether purified intact CMP that is partially glycosylated survives intact to its presumed site of bioactivity within the gut remains unknown.

OBJECTIVES

The aim of this study was to determine the extent to which purified intact CMP (including glycosylated forms) is digested into peptide fragments within the jejunum of healthy human adults after consumption.

METHODS

Jejunal fluids were collected from 3 adult participants (2 men and 1 woman, age: 27 ± 7 y; BMI: 23 ± 1 kg/m2) for 3 h after consuming 37.5 g of purified intact CMP. CMP and CMP-derived peptides were isolated from the collected jejunal fluids by ethanol precipitation and solid-phase extraction and identified by MS-based top-down glycopeptidomics. Relative abundances of CMP and CMP-derived peptides were compared qualitatively between the feed and the jejunal fluids.

RESULTS

Intact CMP was dominant in feeding material, accounting for 90% of the total ion abundance of detected peptides, and in very low abundance (<2%) in the jejunal fluids. CMP-derived fragment peptides ranging from 11 to 20 amino acids in length were predominant (accounting for 68-88% of the total peptide ion abundance) in jejunal fluids during 1-3 h post consumption.

CONCLUSIONS

This study demonstrates that intact CMP (including glycosylated forms) is mostly digested in the human jejunum, releasing a wide array of CMP-derived peptide fragments. Some of the CMP-derived peptides with high homology to known bioactive peptides consistently survived across 3 h of digestion. Therefore, future research should examine the biological effects of the partially digested form-the CMP-derived fragments-rather than those of intact CMP.

Pea-derived peptides, VLP, LLP, VA, and LL, improve insulin resistance in HepG2 cells via activating IRS-1/PI3K/AKT and blocking ROS-mediated p38MAPK signaling

This study evaluated the effect of four peptides, VLP, LLP, LL, and LL from pea on regulating glucose metabolism and antioxidant through IRS-1/PI3K/AKT and p38MAPK signal pathway in IR-HepG2 cell induced by 10-6 M insulin. The genes expression of PEPCK, G6Pase, GLUT2, and IRS-1 and proteins of IRS-1, p(Ser307)-IRS-1, AKT, p(Ser473)-AKT, p38MAPK, and p-p38MAPK were determined by RT-PCR and western blotting, respectively. Results show that they displayed highly potent on stimulation glucose metabolism and relief oxidative stress in IR-HepG2 cells. VLP, LLP, VA, and LL reduced Ser307 phosphorylation of IRS-1 and promoted Ser473 phosphorylation of AKT. Among them, LLP, VA, and LL increased the expression both gene and protein of GLUT2, and VLP and LL reduced p38MAPK phosphorylation showing strong antioxidant capacity. Therefore, pea oligopeptides have considerable potential for reversing the metabolic abnormalities associated with type 2 diabetes. PRACTICAL APPLICATIONS: This paper examined the intervention effect of VLP, LLP, VA, and LL that from pea on insulin resistance, and the mechanisms were detected by western blotting. The results provide a theoretical knowledge for the prevention of insulin resistance in T2D of pea-derived peptides and lay the foundation for the development of functional products and drugs in the future.

Evaluation and Exploration of Potentially Bioactive Peptides in Casein Hydrolysates against Liver Oxidative Damage in STZ/HFD-Induced Diabetic Rats

Hyperglycemia-induced oxidative stress can cause liver damage in diabetes, and protein hydrolysates with antidiabetic and antioxidant properties are emerging as a potential therapy. In this study, protective effects of casein hydrolysates against live oxidative damage in streptozotocin/high-fat-induced diabetic rats were studied and potentially bioactive peptides were explored by an integrated approach of differential peptide and in silico analysis. Results showed that different casein hydrolysates significantly alleviated liver oxidative damage (p < 0.05) via different mechanisms. Particularly, casein hydrolyzed by a papain-flavourzyme combination (P-FCH) treatment significantly improved liver antioxidant enzyme activities by enhancing nuclear factor erythroid 2-related factor 2 (Nrf2) transcription (p < 0.05). Furthermore, 18 peptides were screened as potential bioactive peptides by analyzing differential peptides among different hydrolysates combined with in silico prediction. Among them, the dipeptide WM might directly inhibit the Kelch-like ECH-associated protein 1 (Keap1)-Nrf2 interaction as potential Nrf2 activators. These results suggested that P-FCH might be an alternative way to treat liver damage in diabetes.

Peptides from walnut (Juglans mandshurica Maxim.) protect hepatic HepG2 cells from high glucose-induced insulin resistance and oxidative stress

Schematic of the mechanism underlying the protection of hepatic HepG2 cells against high glucose-induced insulin resistance and oxidative stress by walnut-derived peptides.

Physicochemical characterization, potential antioxidant and hypoglycemic activity of polysaccharide from Sargassum pallidum

A polysaccharide, designated as PSP-1, was isolated and purified from Sargassum pallidum. Physicochemical characterization showed that PSP-1 with the average molecular weight of 1.036 × 106 Da was composed of fucose, arabinose, galactose, glucose, xylose, mannose, galacturonic acid and glucuronic acid in a molar ratio of 18.45:2.15:19.06:1.89:16.07:1.00:5.74:20.09. The results of antioxidant assays indicated that PSP-1 had good DPPH radical scavenging activity, hydroxyl radical scavenging activity, cellular antioxidant activity, and reactive oxygen species inhibition activity, and could significantly improve cellular antioxidant enzymes of ABAP-induced HepG2 cell model. The results of hypoglycemic assays showed that PSP-1 possessed favorable α-amylase and α-glucosidase inhibitory activities, and could remarkably enhance glucose consumption, glycogen synthesis and the activities of pyruvate kinase and hexokinase in insulin-resistance HepG2 cells. The results suggest that PSP-1 can be exploited as a potential antioxidant and hypoglycemic candidate for functional and nutraceutical applications.

Lycopene ameliorates systemic inflammation-induced synaptic dysfunction via improving insulin resistance and mitochondrial dysfunction in the liver-brain axis

Systemic inflammation is an important determinant of synaptic dysfunction, but the underlying molecular mechanisms remain elusive. Lycopene (LYC), a major carotenoid present in tomato, is regarded as a nutraceutical that has significant antioxidant and anti-obesity bioactivities. In the current study, we randomly divided 3-month-old C57BL/6J mice into 3 groups: the control, LPS and LPS + LYC groups (LYC, 0.03% w/w, mixed with normal chow) for 5 weeks, and then mice were intraperitoneally injected with LPS (0.25 mg kg-1) for 9 days. Our results demonstrated that LYC supplementation effectively attenuated LPS-elicited neuronal damage and synaptic dysfunction through increasing the expressions of neurotrophic factors and the synaptic proteins SNAP-25 and PSD-95. LYC ameliorated LPS-induced insulin resistance and mitochondrial dysfunction in the mouse brain and liver. LYC alleviated the neuroinflammation and hepatic inflammation. Furthermore, LYC decreased the circulating levels of insulin and proinflammatory mediators LPS, TNF-α, IL-1β and IL-6. In conclusion, these results indicated that the supplementation of LYC might be a nutritional preventive strategy in systemic inflammation-induced synaptic dysfunction.

Galangin and Pinocembrin from Propolis Ameliorate Insulin Resistance in HepG2 Cells via Regulating Akt/mTOR Signaling

Insulin resistance has a critical role in type 2 diabetes. The aim of this study was to investigate the effect of pinobanksin, galangin, chrysin, and pinocembrin from propolis on insulin resistance. Our study shows that galangin and pinocembrin can ameliorate insulin resistance; on the contrary, pinobanksin and chrysin are ineffective. Galangin and pinocembrin treatments substantially increase glucose consumption and glycogen content by enhancing the activities of hexokinase and pyruvate kinase. Galangin treatment with 80 μM increased hexokinase and pyruvate kinase activities by 21.94% and 29.12%, respectively. Moreover, we hypothesize that galangin and pinocembrin may have a synergistic effect on the improvement of insulin resistance via Akt/mTOR signaling pathway, through distinctly upregulating the phosphorylation of IR, Akt, and GSK3β and remarkably downregulating the phosphorylation of IRS. Most notably, this is the first study to our knowledge to investigate pinocembrin about the alleviation of insulin resistance. Our results provide compelling evidence for the depth development of propolis products to ameliorate insulin resistance.