The genus Landolphia P.Beauv. (Apocynaceae): A comprehensive review on its ethnobotanical utilizations, pharmacology and nutritional potential

ETHNOPHARMACOLOGICAL RELEVANCE

The genus Landolphia is an important resource for African traditional medicine. Among the 60 different accepted species, nearly every plant part of the genus (bark, fruit, latex, leaf, leaf sap, root, rootbark, twig) from 13 species is utilized by traditional healers around Africa. Accordingly, many pharmacological studies (42) were performed on the most common species (11).

AIM OF THE STUDY

This comprehensive literature review summarizes all publications dealing on one of the 60 plant species from the genus Landolphia. An overview about already performed analysis is given and important aspects and knowledge gaps are highlighted for the direction of future research activities.

MATERIALS AND METHODS

A systematic web search taking into account the major platforms Web of Science, Scopus, PubMed, SciFinder and Google Scholar was performed for the term Landolphia. All relevant datasets, published between 1804 and 2022, were ordered according to their topics in different sections and compared to each other. A network visualization of the keywords via VOS Viewer was additionally performed.

RESULTS

In total, 209 publications were retrieved from the search engines, mainly written in English. Predominant are ethnopharmacological studies, which identified 292 phytochemicals in plant parts of the whole genus. Diverse biological activities were detected in different plant extracts, and five species were determined as of special interest for the treatment of malaria. Further research topics identified are botanical aspects, ethnobotanical utilizations, ecological aspects, the potential as source for human and animal nutrition, the manufacturing of rubber, economic aspects, biomechanical studies and others. L. owariensis is the most studied plant as it is abundant in continental Africa.

CONCLUSIONS

This review serves as a database for upcoming research on the genus Landolphia and directs existing knowledge gaps. A wide range of chemical components are already identified, but their exact content in the respective plant parts and their biological activity remains mainly unknown. Utilization patterns from traditional medicine are only partially analyzed as demonstrated for the applications as aphrodisiac, to treat skin diseases or as antidiabetic. Nutritional analyses likewise focus on several species of Landolphia and lack for the wide range of known edible fruits. The demand for new natural products in terms of medicine, rubber and nutrition is still high and the genus Landolphia seems to be a promising resource covering many aspects at once.

Chemical Profile, Antioxidant and Anti-Inflammatory Potency of Extracts of Vitex madiensis Oliv. and Crossopteryx febrifuga (Afzel ex G. Don)

Vitex madiensis Oliv. (Lamiaceae) and Crossopteryx febrifuga (Rubiaceae), two plants commonly used in traditional African medicines to treat malaria and pain, were studied either to determine their chemical profiles or to evaluate their antioxidant and anti-inflammatory activities. In this study, we investigated leaves, trunk bark, root bark and fruits methanolic extracts of both plants in order to find out which part of the plant is responsible for the activity. The analyses of the chemical profiles allowed us to confirm the presence of several ecdysteroids, especially 20-hydroxyecdysone in some parts of V. madiensis and to highlight the presence of organic acids and phenol derivatives in C. febrifuga. Among the four parts of the plants studied, only the fruits extract of C. febrifuga could present anti-inflammatory activity by decreasing ROS production. The leaves and trunk bark extracts of V. madiensis showed significant free radical scavenging activity compared to ascorbic acid, and the same extracts decrease ROS production significantly. The activity of these two extracts could be explained by the presence of ecdysteroids and flavonoids. The ROS production inhibition of V. madiensis is particularly interesting to investigate with further analyses.

Appraising the therapeutical potentials of Alchornea laxiflora (Benth.) Pax & K. Hoffm., an underexplored medicinal herb: A systematic review

Ethnopharmacological relevance: Alchornea laxiflora (Benth.) Pax & K. Hoffm. (Euphorbiaceae) is an important traditional medicinal plant grown in tropical Africa. The stem, leaves, and root have been widely used in the folk medicine systems in Nigeria, Cameroon, South Africa, and Ghana to treat various ailments, including inflammatory, infectious, and central nervous system disorders, such as anxiety and epilepsy. Material and methods: The scientific name of the plant was validated using the "The Plant List," "Kew Royal Botanic Gardens," and Tropicos Nomenclatural databases. The literature search on A. laxiflora was performed using electronic search engines and databases such as Google scholar, ScienceDirect, PubMed, AJOL, Scopus, and Mendeley. Results: To the best of our knowledge, no specific and detailed review has been reported on A. laxiflora. Consequently, this review provides an up-to-date systematic presentation on ethnobotany, phytoconstituents, pharmacological activities, and toxicity profiles of A. laxiflora. Phytochemical investigations disclosed the presence of important compounds, such as alkaloids, flavonoids, phenolics, terpenoids, and fatty acids. Furthermore, various pharmacological activities and traditional uses reported for this botanical drug were discussed comprehensively. Conclusion: This systemic review presents the current status and perspectives of A. laxiflora as a potential therapeutic modality that would assist future researchers in exploring this African botanical drug as a source of novel drug candidates for varied diseases.

In Vitro Cytotoxic Activity of African Plants: A Review

In African countries, cancer not only is a growing problem, but also a challenge because available funding and resources are limited. Therefore, African medicinal plants play a significant role in folk medicine and some of them are traditionally used for the treatment of cancer. The high mortality rate and adverse effects associated with cancer treatments have encouraged the search for novel plant-based drugs, thus, some African plants have been studied in recent years as a source of molecules with proven cytotoxicity. This review aims to discuss the cytotoxic activity, in vitro, of African plant crude extracts against cancer cell lines. For the period covered by this review (2017−2021) twenty-three articles were found and analyzed, which included a total of 105 plants, where the main cell lines used were those of breast cancer (MCF-7 and MDA-MBA-231) and colorectal cancer (HCT-116 and Caco-2), which are among the most prevalent cancers in Africa. In these studies, the plant crude extracts were obtained using different solvents, such as ethanol, methanol, or water, with variable results and IC50 values ranging from <20 µg/mL to >200 µg/mL. Water is the preferred solvent for most healers in African countries, however, in some studies, the aqueous extracts were the least potent. Apoptosis and the induction of cell cycle arrest may explain the cytotoxic activity seen in many of the plant extracts studied. Considering that the criteria of cytotoxicity activity for the crude extracts, as established by the American National Cancer Institute (NCI), is an IC50 < 30 μg/mL, we conclude that many extracts from the African flora could be a promising source of cytotoxic agents.

African Plant-Based Natural Products with Antivirulence Activities to the Rescue of Antibiotics

The worldwide emergence of antibiotic-resistant bacteria and the thread of widespread superbug infections have led researchers to constantly look for novel effective antimicrobial agents. Within the past two decades, there has been an increase in studies attempting to discover molecules with innovative properties against pathogenic bacteria, notably by disrupting mechanisms of bacterial virulence and/or biofilm formation which are both regulated by the cell-to-cell communication mechanism called ‘quorum sensing’ (QS). Certainly, targeting the virulence of bacteria and their capacity to form biofilms, without affecting their viability, may contribute to reduce their pathogenicity, allowing sufficient time for an immune response to infection and a reduction in the use of antibiotics. African plants, through their huge biodiversity, present a considerable reservoir of secondary metabolites with a very broad spectrum of biological activities, a potential source of natural products targeting such non-microbicidal mechanisms. The present paper aims to provide an overview on two main aspects: (i) succinct presentation of bacterial virulence and biofilm formation as well as their entanglement through QS mechanisms and (ii) detailed reports on African plant extracts and isolated compounds with antivirulence properties against particular pathogenic bacteria.