Natural strategies for skin health : bioactivity profiling of plectranthus species with antimicrobial and skin-related enzyme inhibitory activities

Abstract

Plectranthus species have long been valued in traditional medicine for the management of skin-related disorders and are increasingly recognized as promising sources of bioactive compounds with dermatological relevance. Despite their widespread ethnopharmacological use, scientific validation of these properties remains scarce for several species. Therefore, the present study investigated the biological potential of eight Plectranthus species (P. ambiguus (Bolus) Codd, P. barbatus Andrews, P. cylindraceus (Hochst. ex Benth.) A.J. Paton, P. ecklonii Benth., P. fruticosus L'Hér., P. grandidentatus Gürke., P. hadiensis, P. madagascariensis Benth.) in order to substantiate their traditional uses and explore their suitability for dermatological applications. To assess their biological activity, extracts were subjected to a comprehensive evaluation that included general toxicity testing using the Artemia salina lethality assay, antimicrobial screening, and the determination of inhibitory effects against enzymes closely associated with skin ageing and pigmentation processes, namely elastase, collagenase, and tyrosinase. None of the tested extracts exhibited general toxicity in the Artemia salina model, indicating a favourable preliminary safety profile. Antimicrobial activity was mainly directed against Gram-positive bacteria, with Staphylococcus species showing the highest susceptibility. The enzymatic assays highlighted the anti-ageing potential of several extracts. Among them, P. ecklonii and P. cylindraceus displayed the most pronounced elastase inhibitory activity, with IC₅₀ values of 62.82 and 84.76 µg/mL, respectively. Notably, P. ecklonii demonstrated greater inhibitory capacity than the reference compound kojic acid (IC₅₀ = 75.55 µg/mL). In addition, extracts from P. ecklonii, P. grandidentatus, and P. fruticosus showed considerable collagenase inhibition, with IC₅₀ values ranging from 86.62 to 95.93 µg/mL, suggesting their potential to the preservation of skin structure. Collectively, these results provide scientific support for the ethnopharmacological use of Plectranthus species and reinforce their potential as valuable natural sources of bioactive compounds for skin care applications.