Possible Molecular Targets of Cinnamon in the Insulin Signaling Pathway

Cinnamon (CN) is known for its anti-diabetic activities in traditional medicine. CN extracts are reported to have beneficial effects on normal and impaired glucose tolerance, insulin resistance and type-2 diabetes. However, molecular characterization of cinnamon effects is limited. The aim of this study is to observe the effect of CN extract on certain diabetogenes involved in insulin signaling. Streptozotocin (STZ) induced type-2 diabetic rats were given CN extract for one month and its effect was observed on blood glucose levels, body weights and gene expression levels of protein tyrosine phosphatase-1B (PTP-1B), insulin receptor (INSR), insulin receptor substrate-1 (IRS-1), phosphoinositide 3-kinase (PI3K), protein kinase B (PKB), protein kinase C-theta (PKCθ) and phosphoinositide-dependent protein kinase-1 (PDK1) in skeletal muscle and adipose tissue. Statistically significant difference was found in the glucose levels and body weights (p = <0.001; 0.002 respectively) of test and diabetic control groups. In muscle, statistically significant difference was observed in gene expression levels of PTP-1B, IRS-1, PKB, PDK1, PI3K and PKCθ (p = 0.03; <0.001; 0.02; 0.001; 0.01; <0.001 respectively) between test and diabetic control groups and PTP-1B, IRS-1, PKB, PDK1 and PKCθ (p = 0.01; 0.01; 0.03; 0.01; <0.001 respectively) between normal and diabetic control groups. In adipose tissue, statistically significant difference was found in gene expression levels of PTP-1B, PKCθ, IRS-1 (p = <0.001; 0.04; 0.01 respectively) between test and diabetic control groups and PTP-1B, PDK1, PI3K, PKCθ and IRS-1 (p = 0.002; 0.02; 0.02; 0.002; <0.001 respectively) between normal and diabetic control groups. These results suggest that cinnamon normalizes blood glucose level and body weight and affect certain molecular targets in the insulin signaling pathway and therefore, possess strong anti-diabetogenic and hypoglycemic action in HFD and STZ-induced type-2 diabetic rat model. The consistent and / or variable pattern of these genes in skeletal muscle and adipose tissue indicates that cinnamon acts differently by affecting some but not all of these genes and that their expressions are tissue specific. These findings may help to understand the possible molecular mechanism of action of cinnamon and to elucidate its precise role as an anti-diabetic herb.