Flavonoids and its derivatives from Callistephus chinensis flowers and their inhibitory activities against alpha-glucosidase

Abstract

Inhibitors of carbohydrate-hydrolysing enzymes play an important role for the treatment of diabetes. One of the therapeutic methods for decreasing of postprandial hyperglycemia is to retard absorption of glucose by the inhibition of carbohydrate- hydrolysing enzymes, such as α-glucosidase, in the digestive organs. To investigate the therapeutic potential of compounds from natural sources, Callistephus chinensis flowers (CCF) were tested for inhibition of α-glucosidase, and acarboes was used as the positive control. The 70 % ethanol extract of CCF exhibited significant α-glucosidase inhibitory activities with IC50 value of 8.14 μg/ml. The stepwise polarity fractions of CCF were tested further for in vitro inhibition of α-glucosidase. The ethyl acetate (EtOAc) fraction exhibited the most significant inhibitory activity. Eight pure compounds, apigenin, apigenin-7-O-β-D- glucoside, kaempferol, hyperin, naringenin, quercetin, luteolin, and kaempferol-7-O-β-D- glucoside, were isolated (using enzyme assay-guide fractionation method) from the EtOAc fraction. Among these, quercetin was the most active one (IC50 values 2.04 μg/ml), and it appears that the inhibiting percentages are close to acarbose (IC50 values 2.24 μg/ml), the positive control, on α-glucosidase inhibition. HPLC/UV analysis indicated that the major components of CCF are kaempferol, hyperin and quercetin. The presented results revealed that CCF containing these eight flavonoids could be a useful natural source in the development of a novel α-glucosidase inhibitory agent against diabetic complications.

Keywords: Callistephus chinensis flowers; HPLC; alpha-glucosidase; stepwise polarity fractions.

Table 1. Table 1: IC₅₀ values of the fractions and compounds 1-8 from CCF for inhibition of α-glucosidase

Table 2. ¹³C-NMR spectral data for compounds 1-8 (DMSO-d₆) from CCF

Table 3. Linearity of standard curves and sensitivity of compounds 1-8 in CCF

Table 4. Quantities of compounds 1-8 in CCF

Figure 1. α-Glucosidase inhibition by extract, fractions, compounds 1-8 and acarbose:

(a) α-glucosidase inhibition by extract, fractions and acarbose. (b) α-glucosidase inhibition by compounds 1-8 and acarbose. (c) α-glucosidase inhibition by compound 6, EtOAc fraction and acarboes

Figure 2. Structures of compounds 1-8 from CCF

Figure 3. (a) HPLC chromatograms of the mixture of eight pure compounds. (b) HPLC chromatograms of EtOAc-soluble extract. (c) Quantities of compounds 1-8 in CCF