Cassia angustifolia Vahl. Leaves: Determination of Total Phenolic and Sennoside Contents of Different Fractions in Comparison with Their α- Glucosidase and Tyrosinase Inhibitory Effects

Background: Cassia angustifolia Vahl. (Senna) is a medicinal plant containing anthraquinone compounds such as sennoside. Senna is primarily valued for its laxative properties. In Persian medicine, this plant has been also used to treat various disorders such as diabetes and skin hyperpigmentation. Previous studies have shown that different species of senna, such as C. articulata, C. alata, C. Siamea, C. Surattensis inhibit alpha-amylase and α-glucosidase enzymes. To the best of our knowledge, no previous evidence is available on tyrosinase and α-glucosidase inhibitory effects of the extract and different fractions of C. angustifolia leaves. Objectives: The purpose of this study was to investigate the inhibitory effect of the methanol-water extract and different fractions (hexane, chloroform, ethyl acetate, and remaining crude extract) of senna against tyrosinase and α-glucosidase and to investigate their total phenolic and sennoside B contents. Results: Our findings depicted that the methanol-water extract and fractions had no significant anti-tyrosinase activity; however, some fractions were active toward α-glucosidase. The hexane fraction and the remaining crude extract demonstrated the highest inhibition on α-glucosidase compared to acarbose (positive control). In addition, the ethyl acetate fraction contains high phenolic and hydroxy anthraquinone derivatives based on the amount of sennoside B contents equivalent to 382.25 μg/mL of gallic acid and 1.525% of sennoside B, respectively. Moreover, no correlation was observed between the phenolic and sennoside contents of different fractions and their α-glucosidase inhibitory effect. Conclusions: Considering the α-glucosidase inhibition results, the hexane fraction of C. angustifolia can be a valuable fraction for in vitro and in vivo antidiabetic studies as well as further phytochemical studies. Further studies to identify the active substances and the exact mechanism of the bioactive ingredients on the inhibitory effects of α-glucosidase can provide promising results in the future.