Determination of flavonoids from Cirsium japonicum var. maackii and their inhibitory activities against aldose reductase

The therapeutic activities of flavonoids from natural plant sources were investigated. The ethanol extracts from the aerial parts of Cirsium japonicum var. maackii (CJM) were tested for aldose reductase inhibition (ARI). Additionally, stepwise polarity fractions and flavonoids from CJM were evaluated for ARI. The ethyl acetate (EtOAc) fraction from CJM showed significant inhibitory effects. The compounds in the EtOAc fraction were identified as the flavonoids-cirsimaritin (1), hispidulin (2), and cirsimarin (3). Based on an ARI assay, the EtOAc fraction and hispidulin (2) exhibited good AR inhibitory activity (IC50 values of 0.21 μg/mL and 0.77 μM, respectively). An HPLC quantitative analysis of different parts of CJM showed that the aerial part collected in the spring season (CJL1) contains the highest total flavonoid content. These results serve as a basis for maximizing the flavonoid yield and for the efficient usage of various parts of CJM. Our results also suggest that CJM could be a useful ARI material for the treatment of various diabetic complications.