Graphical AbstractScientific validation of South African medicinal plants used traditionally for skin care and their pharmacological properties associated with treating skin conditions. 2

BackgroundAcne vulgaris is a chronic skin disorder leading to inflammation as a result of the production of reactive oxygen species due to the active involvement of Propionibacterium acnes (P. acnes) in the infection site of the skin. The current study was designed to assess the potential of the leaf extract of Syzygium jambos L. (Alston) and its compounds for antibacterial and anti-inflammatory activity against the pathogenic P. acnes.MethodsThe broth dilution method was used to assess the antibacterial activity. The cytotoxicity investigation on mouse melanocyte (B16-F10) and human leukemic monocyte lymphoma (U937) cells was done using sodium 3’-[1-(phenyl amino-carbonyl)-3,4-tetrazolium]-bis-[4-methoxy-6-nitrobenzene sulfonic acid hydrate (XTT) reagent. The non-toxic concentrations of the samples was investigated for the suppression of cytokines interleukin 8 (IL 8) and tumour necrosis factor (TNF α) by testing the supernatants in the co-culture of the human U937 cells and heat killed P. acnes using enzyme immunoassay kits (ELISA). The statistical analysis was done using the Graph Pad Prism 4 program.ResultsBioassay guided isolation of ethanol extract of the leaves of S. jambos led to the isolation of three known compounds namely; squalene, an anacardic acid analogue and ursolic acid which are reported for the first time from this plant. The ethanol extract of S. jambos and one of the isolated compound namely, anacardic acid analogue were able to inhibit the growth of P. acnes with a noteworthy minimum inhibitory concentration (MIC) value of 31.3 and 7.9 μg/ml, respectively. The ethanol extract and three commercially acquired compounds namely; myricetin, myricitrin, gallic acid exhibited significant antioxidant activity with fifty percent inhibitory concentration (IC50) ranging between 0.8-1.9 μg/ml which was comparable to that of vitamin C, the reference antioxidant agent. The plant extract, compounds ursolic acid and myricitrin (commercially acquired) significantly inhibited the release of inflammatory cytokines IL 8 and TNF α by suppressing them by 74 - 99%. TEM micrographs showed the lethal effects of selected samples against P. acnes.ConclusionsThe interesting antibacterial, antioxidant and anti-inflammatory effects of S. jambos shown in the present study warrant its further investigation in clinical studies for a possible alternative anti-acne agent.

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Bioassay-guided fractionation of the methanol extract of the shoots of Myrsine africana led to the isolation of the new compound myricetin 3-O-(2″,4″-di-O-acetyl)-α-l-rhamnopyranoside (9) and 11 known compounds. The known compounds quercetin 3-O-(3″,4″-di-O-acetyl)-α-l-rhamnopyranoside (8), rutin (10), quercetin 3-O-α-l-rhamnopyranoside (11), and myricetin 3-O-α-l-rhamnopyranoside (12) are reported for the first time from the methanol extract of the shoots of M. africana. Compounds 10 and 12 showed significant inhibition of tyrosinase with 50% inhibition (IC values) of the enzyme at 0.13 ± 0.003 and 0.12 ± 0.002 mM, respectively, which was supported by the docking fitness scores obtained through molecular docking analysis. In addition, compounds 1-12 displayed significant antioxidant activity with IC values ranging 1.90 to 3.90 μM.