Traditional usage and biological activity of Plectranthus madagascariensis and its varieties: A review

Abstract

Ethnopharmacological relevance: Plectranthus madagascariensis (Pers.) Benth. is an indigenous aromatic South African plant species that are traditionally used to treat various dermatological and respiratory ailments.

Aim of the study: Three varieties of P. madagascariensis exist in South Africa, namely, Plectranthus aliciae (Codd) van Jaarsv. & T.J. Edwards, Plectranthus ramosior (Benth.) Van Jaarsv. and Plectranthus madagascariensis (Pers.) Benth var. madagascariensis. This article summarizes the documented ethnobotanical uses and research which has been conducted to date on the chemical constituents and biological effects of P. madagascariensis and its varieties. This review aimed to investigate and highlight the lack scientific reports of the potential activity of these varieties based on their traditional usage and to emphasise the need for further investigation of the benefits of P. madagascariensis and its varieties.

Materials and methods: Extensive database retrieval using platforms not limited to but including Google Scholar, ScienceDirect and PubMed, was performed by using keywords such as "Plectranthus madagascariensis" "Plectranthus madagascariensis var. aliciae", "Plectranthus aliciae", "Plectranthus ramosior", "Plectranthus madagascariensis var. ramosior" and "Plectranthus hirtus" In addition, relevant books and digital documentation were consulted to collect all available scientific literature to provide a comprehensive review.

Results: Several studies have reported the traditional usage of P. madagascariensis for the treatment of diseases related to the respiratory system such as coughs, colds and asthma as well as dermatological disorders associated with wounds and inflammation. Whilst there are no reports on the traditional usage of P. madagascariensis varieties to treat other maladies, several other species within the genus are used in other traditional practices. Plectranthus ramosior is used as a toxin for fishing. In literature, seven major phytochemical compounds have been identified from P. madagascariensis. Its extract and essential oil contain polyphenols, abietane diterpenes and abietane diterpenes with a quinone moiety. The extracts and major chemical constituents of P. madagascariensis and its major phytochemicals have reported activity against several biological targets. Reports relating to the antibacterial activity of P. madagascariensis against microbes associated with tuberculosis and wound infections has been consistent and correlates with the documented traditional usage of the plant. Literature reported on the antibacterial activity of P. aliciae targeting bacteria associated with wound infections and lung cancer cells. No further literature reports of the biological activity of the other P. madagascariensis varieties have been found. Other noteworthy biological activities reported in the literature of P. madagascariensis and its compounds include their activities against targets of Alzheimer's disease and breast cancer, in particular. This activity is not related to the traditional usage of the plant.

Conclusion: Plectranthus madagascariensis and its compounds have been proven to be effective in treating a range of maladies. Based on the extensive literature on this plant, it can be concluded that numerous in vitro pharmacological activities of P. madagascariensis have been reported. However, there is a lack of information available for this species with regards to its in vivo data including both pre-clinical and clinical studies. Since the extract of P. madagascariensis and its isolated compounds have displayed noteworthy anticancer potential, we recommend further investigation of pharmacokinetic studies to be included in future research.

Keywords: Biological activity; Ethnobotanical use; Lamiaceae; Phytochemicals; Plectranthus aliciae; Plectranthus hirtus; Plectranthus madagascariensis; Plectranthus madagascariensis var. aliciae; Plectranthus madagascariensis var. madagascariensis.