Polysaccharides from Enteromorpha prolifera Improve Glucose Metabolism in Diabetic Rats

Abstract

This study investigated the effects of polysaccharides from Enteromorpha prolifera (PEP) on glucose metabolism in a rat model of diabetes mellitus (DM). PEP (0, 150, 300, and 600 mg/kg) was administered intragastrically to rats for four weeks. After treatment, fasting blood glucose (FBG) and insulin (INS) levels were measured, and the insulin sensitivity index (ISI) was calculated. The morphopathological changes in the pancreas were observed. Serum samples were collected to measure the oxidant-antioxidant status. The mRNA expression levels of glucokinase (GCK) and insulin receptor (InsR) in liver tissue and glucose transporter type 4 (GLUT-4) and adiponectin (APN) in adipose tissue were determined. Compared with the model group, the FBG and INS levels were lower, the ISI was higher, and the number of islet β-cells was significantly increased in all the PEP groups. In the medium- and high-dose PEP groups, MDA levels decreased, and the enzymatic activities of SOD and GSH-Px increased. The mRNA expression of InsR and GCK increased in all the PEP groups; APN mRNA expression increased in the high-dose PEP group, and GLUT-4 mRNA expression increased in adipose tissue. These findings suggest that PEP is a potential therapeutic agent that can be utilized to treat DM.

Figure 1

Characterization of polysaccharides from Enteromorpha prolifera. (a) shows four peaks in the eluting curve, PEP-1, PEP-2, PEP-3, and PEP-4. The peak area of PEP-2 is the largest and contains 161 mg of polysaccharides. (b) shows the basic graph of PEP-2, which has a single, symmetrical elution peak. (c) shows the wavenumbers of 3386.02 cm⁻¹ as the stretching vibration of O–H, 2923.84 cm⁻¹, 2853.28 cm⁻¹, and 1454.36 cm⁻¹ as the vibration of –CH2–. The 1390.54 cm⁻¹ and 1232.13 cm⁻¹ symmetric stretching vibrations corresponded to two S=O groups of sulfate groups. Furthermore, 848.09 cm⁻¹ and 769.89 cm⁻¹ are the antisymmetric and symmetric stretching vibrations of the sulfate groups C–O and S–O. (d1) shows that the chromatogram of different standard monosaccharides. (d2) shows that PEP-2 is mainly composed of rhamnose, glucuronic acid, arabinose, fucose, xylose, and glucose.

Figure 2

The effect of PEP on OGTT in DM rats. A DM model was established by feeding rats a high-fat diet and injecting them with a low dose of STZ. After the model was established, PEP (0, 150, 300, and 600 mg/kg) was administered intragastrically as an intervention for 28 d (n = 10 rats). Subsequently, the OGTT was performed. Control: control group; Model: model group; Mel HC: metformin HC group; LPEP: low-dose PEP group; MPEP: medium-dose PEP group; HPEP: high-dose PEP group.

Figure 3

The effect of PEP on the histopathological structure of the pancreas in DM rats (H&E staining). A DM model was established by feeding rats a high-fat diet and injecting them with a low dose of STZ. After the model was established, PEP (0, 150, 300, and 600 mg/kg) was administered intragastrically as an intervention for 28 d (n = 10 rats). The pancreatic tissues were collected, embedded, sectioned, and stained with H&E. (a) control: control group; (b) model: model group; (c) metformin HC: metformin HC group; (d) 150 mg/kg: low-dose PEP group; (e) 300 mg/kg: medium-dose PEP group; (f) 600 mg/kg: high-dose PEP group.

Figure 4

The effect of PEP on the histopathological structure of the pancreas in DM rats (IHC). A DM model was established by feeding rats a high-fat diet and injecting them with a low dose of STZ. After the model was established, PEP (0, 150, 300, and 600 mg/kg) was administered intragastrically as an intervention for 28 d (n = 10 rats). The pancreatic tissues were collected, embedded, and sectioned, and a specific antibody against insulin/proinsulin was utilized to observe the residual β-cells in islets by using immunohistochemical method (IHC). (A) control: control group; (B) model: model group; (C) metformin HC: metformin HC group; (D) 150 mg/kg: low-dose PEP group; (E) 300 mg/kg: medium-dose PEP group; (F) 600 mg/kg: high-dose PEP group. The arrow indicates islet tissue. (a) shows the histopathological structure of the pancreas in DM rats by IHC; (b) shows the mean integrated optical density of β-cells in islets in DM rats using the Image-Pro Plus 4.5 image analysis software.

Figure 5

The effect of PEP on the mRNA expression of GCK and InsR in the liver and APN and GLUT-4 in adipose tissue in DM rats. A DM model was established by feeding rats a high-fat diet and injecting them with a low dose of STZ. After the model was established, PEP (0, 150, 300, and 600 mg/kg) was administered intragastrically as an intervention for 28 d. Subsequently, liver and adipose tissue was collected; mRNA was extracted, reverse transcribed into cDNA, and analyzed by real-time PCR to determine the mRNA expression levels in the rats in each group. The mRNA expression levels were determined using the relative quantification method (β-actin was used as the internal control). The data are presented as the mean ± standard deviation (n = 10 rats). Compared with the control group: ^∗ P < 0.05; compared with the model group: ^# P < 0.05.