Antidiabetic compounds from medicinal plants traditionally used for the treatment of diabetes in Africa: A review update (2015–2020)

Abstract

Africa has a rich biodiversity of plants and an active traditional medicine system that takes advantage of the rich biodiversity to treat various diseases, including diabetes mellitus (DM). The folkloric use of some of these plants in treating diabetes has been documented in various databases and publications, and validated with in vitro and in vivo models. In this regard ethnopharmacology remains the major tool in the search for bioactive compounds from African medicinal plants. Our previous review, covering 1977–2014, revealed that fifty-three (53) compounds isolated from African medicinal plants showed varying levels of antidiabetic activity. Since then, several further antidiabetic agents have been isolated from African plants, mostly based on ethnomedicinal information, but they have not been critically reviewed in any previous publication. Therefore, this article provides an insightful commentary on the antidiabetic compounds from African medicinal plants, along with an attempt to highlight the structure-activity relationships. Relevant literature, from 2015 to 2020, was collected by searching the major electronic scientific databases including PubMed, ScienceDirect, Web of Science, and Google Scholar, using appropriate keyword combinations. A total of eighty-four (84) compounds, isolated from different parts of twenty-four (24) African medicinal plants, including, leaves, stem barks, roots, tubers, and aerial parts, were investigated as possible antidiabetic agents. The flavonoids quercetin, kaempferol and apigenin, and the triterpenoids convallatoxin and combretin B are the most promising antidiabetic compounds. In spite of the interesting in vitro and in vivo evidence for antidiabetic activity, not a single compound was investigated in a clinical study. Several compounds from African ethnomedicinal plants have shown promising in vitro or in vivo antidiabetic activity. Some of these compounds are ubiquitous plants metabolites with known non-specific biological activities, but some others are rare phytochemicals that show structure specific bioactivities and should be further investigated. It is hoped that this review would motivate the further studies of these compounds along the drug discovery pipeline. In addition, this review shows that selection of plants based on ethnopharmacological information from African plants is a promising drug discovery strategy.

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