Abstract
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.
Highlights
Acne 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
Antibacterial activity The ethanol extract and compounds were tested against P. acnes by determining the minimum inhibitory concentration (MIC) values obtained by a microdilution method as previously described [9] with few modifications
The compounds isolated from the ethanol extract of leaves of S. jambos were identified as squalene [14] and ursolic acid [15]
Summary
Microbial strain and culture media Silica gel 60 (70–230 mesh); sephadex LH-20 and all the analytical grade chemicals were purchased from SigmaAldrich and Merck SA Pty Ltd. Antibacterial activity The ethanol extract and compounds were tested against P. acnes by determining the minimum inhibitory concentration (MIC) values obtained by a microdilution method as previously described [9] with few modifications. In a sterile 96-well plate, 100 μl of samples from the stock solution consisting of the plant extract/isolated compounds (2 mg/ml in 10% dimethyl sulphoxide (DMSO)) and the positive control tetracycline (0.2 mg/ml) were diluted with broth. Twofold serial dilutions were made in broth over a range to give concentrations of 500–3.9 μg/ml and 50–0.3 and μg/ml for the plant extract/ isolated compounds and positive control tetracycline, respectively. After an overnight incubation at 37°C in 5% CO2 and a humidified atmosphere, the extract, compounds and the positive control (actinomycin D) were added to the cells. IC50 and EC50 values for antioxidant and cytotoxicity tests were derived from a nonlinear regression model (curvefit) based on sigmoidal dose response curve (variable) and computed using GraphPad Prism 4 (Graphpad, San Diego, CA, USA)
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