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In vitro profiling and functional assessments of the anti-diabetic capacity of phenolic-rich extracts of Bulbine natalensis and Bulbine frutescens

Research output: Contribution to journalArticlepeer-review

Sunday O. Oyedemi, Patricio Atanes, Olayinka A. Aiyegoro, Stephen O. Amoo, Shasank S. Swain, Shanta J. Persaud

Original languageEnglish
JournalDiabetic Medicine
Early online date16 Dec 2021
DOIs
Accepted/In press27 Nov 2021
E-pub ahead of print16 Dec 2021

Bibliographical note

Funding Information: The authors thank the South Africa Agency for Science and Technology Advancement for their financial support. Publisher Copyright: © 2021 Diabetes UK

King's Authors

Abstract

Aims

Bulbine natalensis (BN) and Bulbine frutescens (BF) are recommended in South African traditional medicine to treat diabetes, but their modes of action are unknown. This study assessed the phenolic acid profiles, mineral composition and in vitro functional effects of BN and BF to better understand their glucose-lowering capabilities.

Methods

Phenolic acid and mineral composition of BN and BF methanolic extracts were determined by HPLC and inductively coupled plasma optical emission spectroscopy respectively. Antioxidant capacity was assessed by potassium ferricyanide reducing power and 2,2-diphenyl-2-picrylhydrazyl radical scavenging assays, and inhibition of alpha-amylase, alpha-glucosidase, pancreatic lipase and DPP4 was evaluated by standard enzyme assays. The effects of BN and BF extracts on insulin secretion were investigated using static incubations of isolated mouse islets and molecular docking analysis was used to identify interactions of BN and BF with partners that could mediate stimulatory effects on insulin secretion.

Results

Methanolic extracts of BN and BF contained high concentrations of protocatechuic and gallic acids, and high levels of Zn, Mn and Cr. The extracts inhibited alpha-glucosidase, alpha-amylase, pancreatic lipase and DPP4 activities, and they also inhibited free radical generation. Both extracts significantly potentiated glucose-stimulated insulin secretion without significantly affecting basal insulin secretion or islet cell viability. Protocatechuic acid, the most abundant phenolic acid in the extracts, showed high affinity for PKA, PKC, DPP4 and CaMK II in the docking analysis.

Conclusions

BN and BF have multiple beneficial effects on glucoregulatory pathways and they, or their derivatives, could be developed to treat type 2 diabetes.

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