Curcuminoids and Sesquiterpenoids in Turmeric (Curcuma longa L.) Suppress an Increase in Blood Glucose Level in Type 2 Diabetic KK-Ay Mice

Turmeric, the rhizome of Curcuma longa L., has a wide range of effects on human health. The chemistry includes curcuminoids and sesquiterpenoids as components, which are known to have antioxidative, anticarcinogenic, and antiinflammatory activities. In this study, we investigated the effects of three turmeric extracts on blood glucose levels in type 2 diabetic KK-Ay mice (6 weeks old, n = 5/group). These turmeric extracts were obtained by ethanol extraction (E-ext) to yield both curcuminoids and sesquiterpenoids, hexane extraction (H-ext) to yield sesquiterpenoids, and ethanol extraction from hexane−extraction residue (HE-ext) to yield curcuminoids. The control group was fed a basal diet, while the other groups were fed a diet containing 0.1 or 0.5 g of H-ext or HE-ext/100 g of diet or 0.2 or 1.0 g of E-ext/100 g of diet for 4 weeks. Although blood glucose levels in the control group significantly increased (P < 0.01) after 4 weeks, feeding of 0.2 or 1.0 g of E-ext, 0.5 g of H-ext, and 0.5 g of HE-ext/100 g of diet suppressed the significant increase in blood glucose levels. Furthermore, E-ext stimulated human adipocyte differentiation, and these turmeric extracts had human peroxisome proliferator-activated receptor-γ (PPAR-γ) ligand-binding activity in a GAL4-PPAR-γ chimera assay. Also, curcumin, demethoxycurcumin, bisdemethoxycurcumin, and ar-turmerone had PPAR-γ ligand-binding activity. These results indicate that both curcuminoids and sesquiterpenoids in turmeric exhibit hypoglycemic effects via PPAR-γ activation as one of the mechanisms, and suggest that E-ext including curcuminoids and sesquiterpenoids has the additive or synergistic effects of both components. Keywords: Curcuma longa L.; turmeric extract; curcuminoid; sesquiterpenoid; type 2 diabetes; KK-Ay mice; PPAR-γ ligand