Anti-diabetic effects of cinnamaldehyde and berberine and their impacts on retinol-binding protein 4 expression in rats with type 2 diabetes mellitus.
BACKGROUND
Retinol binding protein 4 (RBP4), as an adipocyte secreted cytokine, was recently found to be inversely correlated with expression of glucose transporter 4 (GLUT4) in insulin resistance (IR) state and to have an intimate relationship with IR and type 2 diabetes mellitus (T2DM). The present study aimed to evaluate the anti-diabetic efficacy of cinnamaldehyde (Cin), berberine (Ber), and metformin (Met) as well as their impacts on the RBP4-GLUT4 system.


METHODS
Rat models of T2DM were established by combination of intraperitoneal injection of low-dose streptozotocin and high fat diet induction. Rats were divided into five groups: the control group, the diabetes group, the diabetes + Ber group, the diabetes + Cin group, and the diabetes + Met group. Western blotting was used to detect the serum or tissue RBP4 and GLUT4 protein levels.


RESULTS
After treatment for four weeks, both Cin and Ber displayed significant hypolipidemic, hypoglycemic, and insulin sensitizing functions (P < 0.01) compared with the control group. Their effects on lowering fasting plasma glucose (FPG), low density lipoprotein-cholesterol (LDL-C) and homeostasis model assessment of insulin resistance (HOMA-IR) seem even better than that of Met. Cin and Ber markedly lowered serum RBP4 levels and up-regulated the expression of tissue GLUT4 protein, and Cin seemed more notable in affecting these two proteins.


CONCLUSIONS
Both Cin and Ber display an exciting anti-diabetic efficacy in this study and may be of great value for the treatment of type 2 diabetes. Their mechanisms involve the RBP4-GLUT4 system, during which the serum RBP4 levels are lowered and the expression of tissue GLUT4 protein is up-regulated.
Zhang
Wei
W
Department of Endocrinology, Zhongnan Hospital of Wuhan University, Wuhan, Hubei 430071, China.
Xu
Yan-cheng
YC
Guo
Fang-jian
FJ
Meng
Ye
Y
Li
Ming-li
ML
D000171:Acrolein / Q000031:analogs & derivatives* / Q000627:therapeutic use; D000818:Animals; D001599:Berberine / Q000627:therapeutic use*; D015153:Blotting, Western; D001835:Body Weight; D003924:Diabetes Mellitus, Type 2 / Q000188:drug therapy* / Q000378:metabolism; D051275:Glucose Transporter Type 4 / Q000032:analysis / Q000097:blood; D007004:Hypoglycemic Agents / Q000627:therapeutic use*; D007333:Insulin Resistance; D008055:Lipids / Q000097:blood; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D054839:Retinol-Binding Proteins, Plasma / Q000032:analysis*
D051275:Glucose Transporter Type 4; D007004:Hypoglycemic Agents; D008055:Lipids; C532035:Rbp4 protein, rat; D054839:Retinol-Binding Proteins, Plasma; C495692:SLC2A4 protein, human; D001599:Berberine; D000171:Acrolein; C012843:cinnamaldehyde