Anti-hyperglycemic and Anti-hyperlipidemic Effects of the Triterpenoid-Rich Fractions from Rubus coreanus and Rubus crataegifolius and Their Main Component, Niga-ichigoside , in Streptozotocin-induced Diabetic Rats

To find the antidiabetic activity of the tripterpenoid-rich fractions of Rubus coreanus (TRF-cor) and R. crataegifolius (TRF-cra) leaves or its main component niga-ichigoside $F_1$ (Niga-$F_1$), anti-hyperglycemic and antihyperlipidemic effects were investigated in the diabetic rat model induced by streptozotocin (STZ). Treatments of rats with 200 mg/kg of the TRF-cor, TRF-cra (each, p.o.) or 20 mg/kg of Niga-$F_1$ significantly inhibited the increase of blood glucose concentration about 44.8%, 28.7% or 20.6%, respectively, in the diabetic rats. In addition, treatments with those fractions inhibited the increase of serum concentrations of triglyceride, total cholesterol or LDL-cholesterol caused by STZ. The inhibitory rate on atherogenic index (AI) values of the TRFcor (200 mg/kg), TRF-cra (200 mg/kg) or Niga-$F_1$ (20 mg/kg)-treated groups were decreased about 55.7%, 36.3% or 22.6%, respectively, comparable to STZ-treated group. In the oral glucose tolerance test, treatment of TRF-cor or TRF-cra inhibited the increase of blood glucose concentration in the STZ-induced rats. Administration of 20 mg/kg of Niga-$F_1$ (p.o.) also exhibited similar effects with the effects of both TRFs at 200 mg/kg dose (p.o.). These results support that the triterpenoids, in particular Niga-$F_1$, are contributed to the antidiabetic effects of R. coreanus or R. crataegifolius.