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Anti-oxidant activity, alpha-amylase inhibition and toxicity of leaf extracts of cultivated Rapanea melanophloeos (L.) Mez (cape beech)

N. Lotter, E. Chivandi, B.W. Lembede, A.R. Ndhlala, T.T. Nyakudya, K.H. Erlwanger
South African journal of botany 2019 v.126 pp. 261-264
2,2-diphenyl-1-picrylhydrazyl, Artemia, Fagus, Rapanea melanophloeos, alpha-amylase, anthelmintics, antioxidant activity, bark, diabetes mellitus, enzyme inhibition, flavonoids, free radical scavengers, in vitro studies, inhibitory concentration 50, leaf extracts, leaves, lethal concentration 50, nauplii, proanthocyanidins, screening, toxicity, trees, Southern Africa
Rapanea melanophloeos is a tree indigenous to Southern Africa. Previous work has reported on the potential of the bark and leaf extracts/decoctions as antifungal, anthelmintic and molluscicidal treatments. This study characterised the antidiabetic potential of R. melanophloeos leaf aqueous and methanolic extracts by determining, the antioxidant activity and ability to inhibit the enzyme α-amylase. The safety of the plant was tested in vitro using the brine shrimp assay. The free radical scavenging activity of aqueous and methanolic leaf extracts of R. melanophloeos was determined using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. The methanolic extract showed the highest radical scavenging activity (IC50 = 11.21 ± 0.05 μg/ml). The aqueous extract had highest inhibitory activity against α-amylase with 77.32 ± 1.16% inhibition at a concentration of 1000 μg/ml and IC50 of 126.38 μg/ml compared to that of the methanolic extract (51.62 ± 0.75% inhibition at a concentration of 1000 μg/ml and IC50 of 978.21 μg/ml). Flavonoids, phenols and condensed tannins were present in both the aqueous and methanolic leaf extracts. The LC50 against the brine shrimp nauplii for the aqueous extract was 168.27 μg/ml, while the LC50 for the methanolic extract was 34.91 μg/ml. The preliminary in vitro screening of leaf extracts of R. melanophloeos shows that they contain potentially health beneficial polyphenolics, are non-toxic and may be beneficial in the management of diabetes mellitus.