Abstract
Leucosidea sericea is an evergreen shrub belonging to the Rosaceae family with previous studies that indicated that L. sericea extracts exhibited strong anti-bacterial properties against Propionibacterium acnes, showing potential as a cosmeceutical. The plant is traditionally used as a vermifuge, as an astringent and to treat conjunctivitis. Commercial production is, however, not possible as no information is available on cultivation and the effect of external environmental factors such as seasonal variation on the medicinal properties of the plant. Seasonal variation was investigated and it was found that significant differences were observed between the anti-acne (P. acnes) activity of plant material collected in different seasons. The best activity was found in winter with a mean minimum inhibitory concentration (MIC) of 5.20 μg mL–1 compared to spring at 26.04 μg mL–1. A 1H NMR-based untargeted metabolomic analysis was used to determine the differences in the chemical profiles of plant samples collected in different seasons. Principal component analysis (PCA) showed clear separation of the seasons and a supervised orthogonal partial least square discriminant analysis (OPLS-DA) was used to determine the compounds that differentiated the spring from the winter samples. The contribution plot indicated a strong positive association with the NMR regions from δ 1.2–1.6, 3.3–4.1, and 6.8–8.0 ppm indicative of a compound with an aromatic ring. Different LC-MS analyses were used in conjunction with a compound database, MAGMa and CSIFingerID, which led to the identification of the compound 2-(4-ethoxyphenyl)-5,6,7,8-tetramethoxy-4H-1-benzopyran-4-one and also confirmed the presence of tangeritin, rutin, quercetin glucoside, and kaempferol glucosides as well as several other compounds previously identified from the plant. This compound similar in structure to the anti-microbial flavonoid tangeritin, was only present in the winter samples. It is therefore recommended that seasonal variation be closely monitored during cultivation and commercial harvesting, and that winter is the preferred harvesting season to obtain the best anti-acne activity.
Highlights
Leucosidea sericea Eckl. & Zeyh. is an evergreen dense shrub belonging to the family Rosaceae which includes the genus Rosa, poorly presented in South Africa with L. sericea the sole representative of the genus Leucosidea
Autumn and winter samples grouped close to each other, separated from the summer and spring samples (Figure 1), indicating a similar chemical profile of the samples in winter and autumn when compared to the summer and spring samples
Leucosidea sericea was previously identified as a plant with good activity against P. acnes at 15.62 μg mL−1 and the isolated active compound α-kosin with an minimum inhibitory concentration (MIC) value of 1.95 μg mL−1 (Sharma et al, 2014)
Summary
Leucosidea sericea Eckl. & Zeyh. is an evergreen dense shrub belonging to the family Rosaceae which includes the genus Rosa, poorly presented in South Africa with L. sericea the sole representative of the genus Leucosidea. The tree occurs in mountainous areas near water at high altitudes of 1000 m in parts of Africa such as Zimbabwe and Lesotho. It is commonly known as “oldwood” (English), “ouhout” (Afrikaans), and “umTshitshi” in Zulu, and traditionally used as a charm to protect the inhabitants of homesteads, treat various ailments such as opthalmia and intestinal worm infection, used as a vermifuge and astringent. The anti-acne activity for L. sericea was reported with a MIC value of 15.62 μg mL−1 and the isolated active compound α-kosin with an MIC value of 1.95 μg mL−1 (Sharma et al, 2014), and presents and opportunity as an anti-acne cosmeceutical
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