Anti-acne and anti-hyperpigmentation potential of selected South African bryophytes with identification of oleamide as a lead compound

Abstract

Acne vulgaris (AV), a chronic dermal inflammatory condition, affects approximately 9.4 % of the global population, with adolescents exhibiting the highest prevalence. Cutibacterium acnes is a key pathogenic factor in this chronic inflammatory condition, often resulting in post-inflammatory hyperpigmentation (PIH), which is primarily treated with tyrosinase inhibitors targeting melanin synthesis. While bryophytes are underexplored in modern cosmeceutical research, they have a history of use in traditional Chinese and Indian medicine for skin ailments. This study aimed to evaluate the antibacterial and anti-tyrosinase potential of three bryophyte species—Bryum argenteum Hedw., Fabronia pilifera Hornsch., and Leptodictyum riparium (Hedw.) Warnst.—to assess their utility in managing AV and PIH. Ethanolic (70 % v/v) extracts were prepared from rinsed and unrinsed plant material. Antibacterial activity against C. acnes (ATCC 6919) was assessed via PrestoBlue microtiter plate assays to determine the minimum inhibitory concentration (MIC) of the bryophyte ethanolic extracts. Tyrosinase inhibition was measured using colorimetric microtiter plate assays to evaluate anti-hyperpigmentation potential. Lead extracts were further analysed for their volatile constituents using gas chromatography-mass spectrometry (GC-MS). Rinsed B. argenteum extract exhibited the strongest antibacterial activity with an MIC of 31.25 μg/mL, followed by rinsed F. pilifera extract at 62.5 μg/mL. All extracts showed minimal tyrosinase inhibition, with IC₅₀ values exceeding the highest concentration tested. GC-MS analysis identified oleamide, a compound with known antibacterial properties, as the major volatile constituent (17.37 %–52.64 %), with the highest concentration of oleamide found in rinsed B. argenteum extract. These findings suggest that selected bryophytes, particularly B. argenteum, may serve as promising sources of antibacterial agents for the treatment of AV. Although pharmaceutically significant tyrosinase inhibition was not observed, the high oleamide content warrants further investigation through bioassay-guided fractionation. This study introduces bryophytes as novel candidates for cosmeceutical applications targeting acne-related skin concerns.

HIGHLIGHTS • Determination of antibacterial activity of selected bryophyte species. • Variation in bioactivity and chemical profile between bryophyte extract preparations. • Antibacterial (Cutibacterium acnes) activity of rinsed Bryum argenteum and Fabronia pilifera with MICs of 31.25 μg/mL and 62.5 μg/mL respectively. • Oleamide is the primary volatile constituent of 70 % ethanolic B. argenteum and F. pilifera extracts.