In vitro antibacterial and anti-inflammatory effects of honokiol and
magnolol against Propionibacterium sp.

Junho Park1, Jongsung Lee1, Eunsun Jung, Yumi Park, Kukhyun Kim,
Byunghwa Park, Kwangseon Jung, Eunkyung Park, Jieun Kim and Deokhoon
ParkCorresponding Author Contact Information, E-mail The Corresponding
Author
Biospectrum Life Science Institute, Doosan Building, 39-3 Sungbok-
dong, Yongin, 449-840 Kyunggi-do, South Korea
Received 27 October 2003;  accepted 19 May 2004.  Available online 29
July 2004.

Abstract

Honokiol and magnolol, two major phenolic constituents of Magnolia
sp., have been known to exhibit antibacterial activities. However,
until now, their antibacterial activity against Propionibacterium sp.
has not been reported. To this end, the antibacterial activities of
honokiol and magnolol were detected using the disk diffusion method
and a two-fold serial dilution assay. Honokiol and magnolol showed
strong antibacterial activities against both Propionibacterium acnes
and Propionibacterium granulosum, which are acne-causing bacteria. The
minimum inhibitory concentrations (MIC) of honokiol and magnolol was 3-
4 μg/ml (11.3-15 μM) and 9 μg/ml (33.8 μM), respectively. In addition,
the killing curve analysis showed that magnolol and honokiol killed P.
acnes rapidly, with 105 organisms/ml eliminated within 10 min of
treatment with either 45 μg (169.2 μM) of magnolol or 20 μg (75.2 μM)
of honokiol per ml. The cytotoxic effect of honokiol and magnolol was
determined by a colorimetric (3-(4,5-dimetyl-2-thiazolyl)-2,5-
diphenyl-2H-tetrazolium bromide) (MTT) assay using two animal cell
lines, human normal fibroblasts and HaCaT. In this experiment,
magnolol exhibited lower cytotoxic effects than honokiol at the same
concentration, but they showed similar cytotoxicity when triclosan was
employed as an acne-mitigating agent. In addition, they reduced
secretion of interleukin-8 and tumor necrosis factor α (TNF-α) induced
by P. acnes in THP-1 cells indicating the anti-inflammatory effects of
them. When applied topically, neither phenolic compound induced any
adverse reactions in a human skin primary irritation test. Therefore,
based on these results, we suggest the possibility that magnolol and
honokiol may be considered as attractive acne-mitigating candidates
for topical application.

Author Keywords: Antibacterial; Anti-inflammatory; MIC (Minimum
inhibitory concentration); MBC (Minimum bactericidal concentration);
Irritation

Corresponding Author Contact InformationCorresponding author. Tel.:
82-31-266-4601; fax: 82-31-263-9609.

1 Junho, P. and Jongsung, L. contributed equally to this work.
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