In vitro antioxidant, cytotoxic, phytotoxic and α-amylase inhibitory potential of four Sri Lankan medicinal plants

Abstract

Plants are rich in secondary metabolites that have many physiological effects. This study determined the bioactivities of four widely distributed plants in Sri Lanka. Leaves of Canna indica (Cannaceae/ Buthsarana), Muntingia calabura (Muntingiaceae/ Jam), Piper betle (Piperaceae/ Nagawalli) and Pongamia pinnata (Leguminosae/ Karada) were collected from Kandy, Sri Lanka. They were shade-dried, ground and extracted into methanol by sonication. The antioxidant potential of crude extracts was determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and ferric reducing antioxidant power (FRAP) assays, antidiabetic activity by α-amylase inhibitory assay, cytotoxicity by brine shrimp lethality assay and phytotoxicity by the lettuce seed germination assay. The results revealed that M. calabura has a strong antioxidant potential (IC₅₀ 6.84 ± 0.12 mg/L) compared to the positive control, ascorbic acid (IC₅₀ 1.97 ± 0.06 mg/L). The IC₅₀ values of C. indica, P. betle and P. pinnata were 1085.72 ± 100.5 mg/L, 49.86 ± 3.15 mg/L and 182.92 ± 21.34 mg/L respectively. When compared to the positive control, Trolox (12.07 ± 0.30 μmol/dm³ FeSO₄/g), none of the crude extracts resulted in high FRAP values ranging between 0.2 – 1.8 μmol/dm³ FeSO₄/g. In α-amylase inhibitory assay, leaves of M. calabura resulted in an IC₅₀ of 84.43 ± 2.32 mg/L with no significant difference with positive control, acarbose (IC₅₀ 45.99 ± 3.97 mg/L). The IC₅₀ values of P. betle and P. pinnata were 796.00 ± 43.67 mg/L and 1394.94 ± 101.23 mg/L, while no activity was detected for C. indica. In the brine shrimp lethality assay, M. calabura, P. betle, and P. pinnata showed LC₅₀ of 540.01 ± 6.76 mg/L, 856 ± 14.72 mg/L and 771.04 ± 8.55 mg/L, respectively, while C. indica resulted in 0% lethality. Whereas the positive control, K₂Cr₂O7, resulted in LC₅₀ 35.16 ± 4.22 mg/L. In the phytotoxicity assay, the IC₅₀ for root inhibition of M. calabura, C. indica, P. betle and P. pinnata were 319.21 ± 10.35 mg/L, 63.9 ± 4.30 mg/L, 70.98 ± 1.42 mg/L and 297.59 ± 8.97 mg/L respectively. The IC₅₀ of shoot inhibitions were 704.72 ± 9.92 mg/L, 265.09 ± 12.57 mg/L, 178.13 ± 8.87 mg/L and 470.78 ± 14.62 mg/L respectively. The positive control, abscisic acid, had a root inhibition of 0.29 ± 0.03 mg/L and shoot inhibition of 0.25 ± 0.01 mg/L. These results revealed that M. calabura crude extract has strong antioxidant and antidiabetic activity, and C. indica leaves have strong root inhibition potential.