Protective effects of di- and tri-peptides containing proline, glycine, and leucine on liver enzymology and histopathology of diabetic mice

CONTEXT

Small peptides as multifunctional biomolecules can prevent the metabolic disorders such as diabetes.

OBJECTIVE

The purpose of this study was to investigate the effects of small peptides on the enzymes and histopathology of the liver in mice exposed to diabetes.

METHODS

Di- and tri-peptides containing proline, glycine, and leucine were produced by solid phase peptide synthesis (SPPS) protocol. The effects of produced peptides as well as carnosine (Ala-His) and glutathione (Glu-Cys-Gly) were evaluated on hepatic enzymes activity by enzymatic method and histopathology of liver using hematoxylin and eosin and TUNEL staining to assess histologic changes and apoptosis in diabetes induced by multiple low doses of streptozotocin (MLDS).

RESULTS

The Ala-His, Leu-Gly and Pro-Gly-Pro peptides had the higher protective effects against the effects of diabetes on the enzymes and histologic changes of liver in mice.

CONCLUSION

These peptides can be raised as considerable pharmaceutical preventive agent against diabetes development.

Effect of a New Synthetic Peptide Preparation AСTH15-18PGP on the Hemostasis System in Rats

We studied the effect of chronic intranasal and peroral administration of a new peptide preparation AСTH_15-18PGP in a dose of 100 mg/kg body weight on the state of vascular-platelet and plasma hemostasis in animals. It was found that this synthetic regulatory peptide administered intranasally can produce antiplatelet, anticoagulant, and antifibrin-stabilizing effects on the blood plasma in healthy rats. In both administration routes, the peptide induced activation of the anticoagulation system of the hemostasis by increasing enzymatic and non-enzymatic fibrinolysis; after intranasal administration, the fibrinolytic effects were more pronounced.

Studying the Toxic Effects of Some Biologically Active Peptides on the Model of Mouse Embryonic Stem Cells

We studied the effects of peptide drugs (HLDF-6, PGP, RPGP, and PGLP) and peptide pharmaceutical products (Semax, Selank, and thyroliberin) on proliferation and survival of mouse embryonic stem cells and their derivatives. Differentiation of mouse embryonic stem cells into neuronal precursors was evaluated. PGP and PGLP in concentrations of 10 and 0.1 μM, respectively, had little, but significant inhibitory effect on proliferative activity of cells. These peptides in concentrations of 10 and 0.1 μM, respectively, and Semax (10 and 0.1 μM) significantly increased the survival rate of mouse embryonic stem cells (serum deprivation). Moreover, study peptides had little effect on the formation of neuronal precursors from mouse embryonic stem cells. HLDF-6, Selank, and thyroliberin produced an insignificant effect on the differentiation of these cells into mature neurons. Analysis of differentiation of embryonic stem cells into GABA⁺ neurons showed that Selank, thyroliberin (100 μM), and NGF (100 ng/ml) decrease the ratio of these cells by 61, 58, and 87%, respectively, in comparison with the control. Our results indicate that these peptide compounds do not produce toxic effect during the embryonic and fetal period of life.

Dietary fish protein hydrolysates containing bioactive motifs affect serum and adipose tissue fatty acid compositions, serum lipids, postprandial glucose regulation and growth in obese Zucker fa/fa rats

The world's fisheries and aquaculture industries produce vast amounts of protein-containing by-products that can be enzymatically hydrolysed to smaller peptides and possibly be used as additives to functional foods and nutraceuticals targeted for patients with obesity-related metabolic disorders. To investigate the effects of fish protein hydrolysates on markers of metabolic disorders, obese Zucker fa/fa rats consumed diets with 75 % of protein from casein/whey (CAS) and 25 % from herring (HER) or salmon (SAL) protein hydrolysate from rest raw material, or 100 % protein from CAS for 4 weeks. The fatty acid compositions were similar in the experimental diets, and none of them contained any long-chain n-3 PUFA. Ratios of lysine:arginine and methionine:glycine were lower in HER and SAL diets when compared with CAS, and taurine was detected only in fish protein hydrolysate diets. Motifs with reported hypocholesterolemic or antidiabetic activities were identified in both fish protein hydrolysates. Rats fed HER diet had lower serum HDL-cholesterol and LDL-cholesterol, and higher serum TAG, MUFA and n-3:n-6 PUFA ratio compared with CAS-fed rats. SAL rats gained more weight and had better postprandial glucose regulation compared with CAS rats. Serum lipids and fatty acids were only marginally affected by SAL, but adipose tissue contained less total SFA and more total n-3 PUFA when compared with CAS. To conclude, diets containing hydrolysed rest raw material from herring or salmon proteins may affect growth, lipid metabolism, postprandial glucose regulation and fatty acid composition in serum and adipose tissue in obese Zucker rats.

Casein glycomacropeptide-derived peptide IPPKKNQDKTE ameliorates high glucose-induced insulin resistance in HepG2 cells via activation of AMPK signaling

SCOPE

Recently, casein glycomacropeptide (GMP)-derived peptide was found to possess potent antioxidant and anti-inflammatory activities. In this study, the improvement effects and underlying molecular mechanisms of GMP-derived peptide on hepatic insulin resistance were investigated.

METHODS AND RESULTS

The peptide IPPKKNQDKTE was identified from GMP papain hydrolysates by LC-ESI-MS/MS. Effects of IPPKKNQDKTE on glucose metabolism and expression levels of the hepatic insulin signaling proteins in high glucose-induced insulin-resistant HepG2 cells were evaluated. Results showed that IPPKKNQDKTE dose-dependently increased glucose uptake and intracellular glycogen in insulin-resistant HepG2 cells without affecting cell viability. IPPKKNQDKTE increased the phosphorylation of Akt and GSK3β and decreased the expression levels of p-GS, G6Pase and PEPCK. These IPPKKNQDKTE-mediated protection effects were reversed by PI3K/Akt inhibitor LY294002, showing the mediatory role of PI3K/Akt. Moreover, treatment with IPPKKNQDKTE reduced IRS-1 Ser307 phosphorylation and increased phosphorylation of AMPK. Knockdown AMPK using siRNA in HepG2 cells increased Ser307 phosphorylation of IRS-1 and reduced Akt phosphorylation in IPPKKNQDKTE-treated insulin-resistant cells.

CONCLUSION

IPPKKNQDKTE prevents high glucose-induced insulin resistance in HepG2 cells by modulating the IRS-1/PI3K/Akt signaling pathway through AMPK activation, indicating that IPPKKNQDKTE plays a potential role in the prevention and treatment of hepatic insulin resistance and type 2 diabetes.

Mechanisms for glyproline protection in hypercholesterolemia

Comparative analysis of the hypocholesterolemic and antithrombotic action of small regulatory glyproline peptides (Pro-Gly-Pro, Arg-Pro-Gly-Pro and Pro-Gly-Pro-Leu) was performed on an experimental hypercholesterolemia model of rats. Repeated intranasal introduction of glyproline peptides to fat-diet-fed animals led to more active functioning of the anticoagulation system (the anticoagulant and fibrinolytic properties of the plasma increased and platelet aggregation decreased) and to normalization of the total cholesterol level as a parameter of lipid metabolism. The largest anticoagulant and hypocholesterolemic effect was detected for the Pro-Gly-Pro-Leu peptide. Hypothetical mechanisms of antithrombotic and hypocholesterolemic effects of glyproline peptides are presented.