Abstract
The stem bark (SB) of Piptadeniastrum africanum (PA) has been extensively used in African traditional medicinal systems. However, there is a dearth of scientific information regarding its possible activity in the management of type II diabetes, Alzheimer’s disease, and skin hyperpigmentation disorders. This study therefore attempted to elucidate the in vitro inhibitory action of ethyl acetate, methanol, and water extracts of P. africanum stem bark (PA-SB) on α-amylase, α-glucosidase, acetylcholinesterase, butyrylcholinesterase, and tyrosinase. Cell viability, catecholamine, and 3-hydroxykynurenine levels of hypothalamic HypoE22 cells exposed to PA-SB extracts were also investigated. The phytochemical profiles of the extracts were determined by high performance liquid chromatography (HPLC) and antioxidant properties were investigated. Saponin (867.42 mg quillaja equivalent/g) and tannin (33.81 mg catechin equivalent/g) contents were higher in the methanol extract. Multiple dihydroxy-trimethoxy(iso)flavone isomers, loliolide, eriodictyol, naringenin, luteolin, chrysoeriol, apigenin, and liquiritigenin, were characterized from PA-SB extracts using HPLC. The methanol extract of PA-SB showed highest inhibitory activity against acetylcholinesterase (4.88 mg galantamine equivalent (GALAE)/g extract), butyrylcholinesterase (5.37 mg GALAE/g extract), and tyrosinase (154.86 mg kojic acid equivalent/g extract) while α-glucosidase was effectively inhibited by the ethyl acetate extract (15.22 mmol acarbose equivalent/g extract). The methanol extract of PA-SB also showed potent antioxidant properties (493.87, 818.12, 953.07, and 732.19 mg Trolox equivalent/g extract, for 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS), cupric reducing antioxidant capacity (CUPRAC), and ferric reducing antioxidant power (FRAP) assays, respectively). PA-SB extracts exhibited antioxidant activity and promising inhibition against key enzymes related to type II diabetes, Alzheimer’s disease, and skin hyperpigmentation disorders. Additionally, all extracts were able to contrast hydrogen peroxide-induced oxidative stress, in HypoE22 cells, thus restoring basal catecholamine and 3-hydroxykinurenine levels, whereas only methanol and water extracts stimulated basal dopamine release. Overall, data from the present study contribute to the biological assessment of P. africanum that appears to be a promising source of natural compounds with protective and neuromodulatory effects.
Highlights
Piptadeniastrum africanum (Hook.f.) Brenan (Mimosaceae), a massive tree which can reach up to 50 m, is widely distributed across Western Africa tropical rainforests of Angola, Uganda, Senegal Cameroon, Democratic Republic of Congo, Nigeria, and Sudan [1]
Dlamini and colleagues (2019) summarized the ethnomedicinal uses of P. africanum across different countries in Africa. They reported that in Nigeria the stem bark and root were used to treat sickle cell anemia and cancer, respectively; in Guinea the stem bark is used for its antibacterial properties, whereas leaves are used in the management of diabetes; in Ghana, Benin, and Gabon the bark is used for waist pain impotence [1]
The analysis of P. africanum stem bark showed that the methanol and water extracts were rich in phenolic, phenolic acids, and tannins (Table 1)
Summary
Piptadeniastrum africanum (Hook.f.) Brenan (Mimosaceae), a massive tree which can reach up to 50 m, is widely distributed across Western Africa tropical rainforests of Angola, Uganda, Senegal Cameroon, Democratic Republic of Congo, Nigeria, and Sudan [1]. Dlamini and colleagues (2019) summarized the ethnomedicinal uses of P. africanum across different countries in Africa As such, they reported that in Nigeria the stem bark and root were used to treat sickle cell anemia and cancer, respectively; in Guinea the stem bark is used for its antibacterial properties, whereas leaves are used in the management of diabetes; in Ghana, Benin, and Gabon the bark is used for waist pain impotence [1]. Mbiantcha and co-workers have reported the antiarthritic activity of methanol and aqueous extracts of P. africanum stem bark in Freund’s adjuvant induced arthritis rat model. Antifungal activity (Pyricularia grisea) was observed for aqueous and methanol extracts of P. africanum stem bark. Isolation of tannin and saponin from P. africanum stem bark methanol extract revealed promising activity against five different Pyricularia grisea strains [3]. In HypoE22 cells, we investigated extract effects on extracellular levels of 3-hydroxykinurenine (3-HK), a recognized marker of neurotoxicity [10]
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