Collagen peptides alleviate hyperglycemia in mice by ...

Introduction

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disorder characterized by persistent hyperglycemia, insulin resistance, and impaired insulin secretion [1]. A prominent symptom is a significant elevation in fasting blood glucose levels of patients. Dipeptidyl peptidase-IV (DPP-IV) inhibitors, known for enhancing insulin responses and reducing hyperglycemia, have emerged as promising targets for intervening in T2DM [2]. Currently, DPP-IV inhibitors such as Saxagliptin and Sitagliptin are utilized in clinical settings to alleviate T2DM, demonstrating a notable effect in lowering fasting blood glucose levels [3]. However, the widespread use of these synthetic drugs may lead to hepatic damage, resulting in complications for T2DM patients [4]. Thus, there is a requirement to create food-derived DPP-IV inhibitors to alleviate the side effects associated with synthetic medications. One possible approach entails acquiring low molecular weight peptides to hinder DPP-IV activity and improve the regulation of blood glucose levels.

Collagen peptides, which are rich in proline and arginine, have been identified as effective DPP-IV inhibitors [5]. Previous studies have predominantly focused on screening and characterizing these peptides, with in vitro assessments of the bioavailability of active peptides often involving simulated gastrointestinal digestion. However, this method provides limited insights into the suitability of peptides within the complex gastrointestinal environment and their regulatory mechanisms in vivo. Therefore, current efforts are directed towards further validating the glucose-lowering efficacy of both pharmaceuticals and natural dietary supplements through the development of in vivo models.

The body maintains blood glucose levels through a delicate equilibrium between the production, transport, and utilization of glucose. In individuals with T2DM, the gluconeogenesis process becomes excessively active, while insulin secretion by pancreatic beta cells is markedly deficient, and closely linked to key kinases in the body [6]. Adenosine monophosphate-activated protein kinase (AMPK) serves as a kinase and energy sensor crucial for regulating glucose homeostasis and insulin sensitivity [7]. The phosphorylation and activation of AMPK (p-AMPK) reduce blood glucose levels and help stabilize glucose levels by modulating key enzymes involved in gluconeogenesis such as pyruvate carboxylase (PC), phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6-phosphatase (G6Pase) [8]. Elevated activity of key gluconeogenic enzymes promotes hepatic glucose output, inducing insulin resistance (IR) and increasing fasting blood glucose levels. Various plant extracts, including black onion polysaccharide, black mulberry extract, sulforaphane, and quinoa protein hydrolysate, have demonstrated significant mitigating effects in T2DM by reducing blood glucose levels, enhancing glucose tolerance, improving insulin resistance, and inhibiting oxidative stress in type 2 diabetic rats [[9], [10], [11], [12]].

Recent studies have confirmed that plant extracts alleviate T2DM symptoms by reducing glucose absorption in the body through the regulation of α-amylase and α-glucosidase activity [9]. Notably, dipeptidyl peptidase IV (DPP-IV) is an enzyme that inhibits insulin secretion by degrading incretins (glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1), leading to elevated blood glucose levels [10]. Proline-and arginine-rich collagen peptides are effective inhibitors of DPP-IV, meanwhile, the use of cowhide collagen peptides to alleviate T2DM through the regulation of insulin sensitivity and glucose metabolism has not been reported. Therefore, it is essential to establish a T2DM model to investigate whether collagen peptides can modulate insulin resistance, gluconeogenesis, and glycogen synthesis through AMPK-mediated signaling pathways, thereby improving T2DM and regulating lipids, gut microbiota, and organ damage.

In this study, a T2DM mice model was induced by administering a high-fat diet in combination with streptozotocin (STZ). Subsequently, the effects of different doses of collagen peptides intervention on mouse morphology, organ index, water and food intake, blood glucose and lipid levels, and the expression of key proteins involved in glucose metabolism and insulin signaling pathways such as AMPK, p-AMPK, PEPCK, FoxO1, GSK3β, p-GSK3β and IRS1 were investigated. Moreover, 16S rDNA sequencing and gas chromatography–mass spectrometry (GC–MS) were performed to assess the gut microbiota and short-chain fatty acids (SCFAs).

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Materials and chemicals

High-fat feed (35 % fat) and Streptozotocin (STZ) were procured from Beijing Boaigang Biotechnology Co., Ltd. (Beijing, China), while the normal diet was sourced from the Laboratory Animal Centre of Lanzhou Institute of Veterinary Medicine, Chinese Academy of Agricultural Sciences (Lanzhou, China). Glucose was supplied by Sinopharm Chemical Reagent Co., Ltd., and hematoxylin and eosin were obtained from Beijing Prilosec Gene Technology Co., Ltd. Metformin was sourced from Sino-US Shanghai

Effects of collagen peptides on morphology, feeding and drinking in mice

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disorder characterized by symptoms such as excessive thirst, increased appetite, frequent urination, and weight loss. The amelioration of these symptoms is often considered indicative of successful mitigation of diabetes and its complications [15]. In this study, we extracted low molecular weight (<1 kDa) peptides that with high DPP-IV inhibitory activity (IC50 of 3.04 ± 0.13 mg/mL) from cowhide collagen [5], and investigated the

Conclusion

The administration of collagen peptides in T2DM mice effectively alleviated T2DM symptoms by regulating blood glucose levels, improving dyslipidemia, and reducing organ damage. Collagen peptides activated AMPK, increased IRS1 expression, and stimulated the PI3K/Akt pathway, which led to the upregulation of p-GSK3β expression and promoted glycogen synthesis. Additionally, collagen peptides inhibited FoxO1 and PEPCK expression, effectively suppressing gluconeogenesis and lowering hepatic glucose

CRediT authorship contribution statement

Long He: Writing – original draft, Methodology, Data curation. Yongfang Gao: Investigation. Chaoqiang Ju: Writing – review & editing. Xinyue Wang: Data curation. Yueyue Zhang: Software. Qunli Yu: Writing – review & editing, Project administration, Funding acquisition. Li Zhang: Supervision, Resources. Cheng Chen: Writing – review & editing. Yufeng Duan: Investigation.

Declaration of competing interest

The authors declare no conflict of interest.

Acknowledgement

This work was supported by the National Natural Science Foundation of China (32460559), the Project of Doctoral Research Initiation Fund (GAU-KYQD-2023-15), the Natural Science Foundation of Gansu Province (24JRRA647 and 22JR5RA711), the Agriculture Research System of China (CARS-37). We thank the editor and reviewer for their valuable comments and suggestions on an earlier draft of this manuscript.