Matrix metalloproteinases (MMPs) are enzymes that can degrade various proteins comprising
the extracellular matrix (ECM) [1]. They are well known for their close relationship
with cancer metastasis and skin aging [2]. More than 20 MMPs have been reported so
far, and these include major gelatinases (MMP-2 and MMP-9) and collagenases (MMP-1,
MMP-8, and MMP-13) [2], [3], [4]. The collagenases have the very specialized ability
to destroy the collagen triple helix. As a result, collagen chains are unwound to
be further destroyed by other MMPs. Particularly, MMP-1 is the most abundant of these
collagenases and breaks down collagen types 1, 2, and 3 [1]. Among the various protein
components comprising the ECM, collagen is the most abundant [5]. The ECM functions
as a physical and biochemical barrier for cells migrating from their original site and
maintains the structural integrity of the skin dermis [6]. Therefore, degradation
of collagen is a critical step in cancer cell metastasis and a major cause of skin
aging.
In Northeast Asian countries including Korea, China, and Japan, Korean ginseng has
been regarded as a valuable herbal medicine. Ginsenosides are the major active components
exerting pharmacological characteristics of ginseng. Of the ginsenosides known so
far, Rb1 ginsenoside from Panax ginseng is the most abundant one and the source of
ginsenoside compound K [7]. Compound K (CK), 20-O-b-D-glucolyranosyl-20(S)-protopanaxadiol,
was first isolated from soil bacteria [7], [8], [9], [10], [11] (Fig. 1A). Among the
many biological functions investigated so far, the skin protective effects of CK through
the inhibition of MMP-1 has drawn attention of researchers [10], [12], [13].
Fig. 1
Inhibitory effect of maclurin on collagenase activity in HaCaT human keratinocyte
cells. (A) Chemical structure of CK. (B) Chemical structure of maclurin. (C) Collagenase
activity of MMP-1 was inhibited by maclurin in HaCaT human keratinocyte cells. (D)
Cytotoxicity of maclurin was tested. Cell viability was assayed using the CCK-8 Kit.
The results were statistically evaluated using Student t test. *p < 0.05; **p < 0.01.
CCK-8, Cell Counting Kit-8; CK, compound K; MMP, matrix metalloproteinase.
Maclurin [(3,4-dihydroxyphenyl)-(2,4,6-trihydroxyphenyl)methanone] is a natural compound
belonging to the benzophenone family and is ethanol-extracted from Morus alba and
Garcinia mangostana (Fig. 1B). Maclurin was reported as one of the five major phenolic
components of the ethanol extract of mulberry twigs (resveratrol, rutin, morin, isoquercitrin,
and maclurin) and found to possess antioxidative activity via the inhibition/reduction
of superoxide [14]. It was reported earlier that maclurin has antimetastatic effects
in human non–small cell lung cancer cells via inhibitions of two major gelatinases,
MMP-2 and MMP-9 [15]. The inhibitory effect on these two metalloproteinases was closely
related to the suppression of the transcriptional expression of both MMP-2 and MMP-9.
Based on this phenomenon, maclurin was suggested to be developed as a potential antimetastatic
agent for various tissue-specific human cancers. In this study, I decided to link
the suppressive effect of maclurin on MMPs to the development of functional agents
for the prevention of skin aging. Because mulberry twigs are agricultural waste, maclurin
would be a relatively inexpensive and environment-friendly material to be used in
combination with relatively costly CK. To test the possibility to be used as synergistic
material on CK-induced MMP-1 inhibition, the inhibitory effect of maclurin on MMP-1
was investigated in HaCaT human keratinocyte cells. Because collagens are the most
abundant proteins comprising the ECM, which gets broken down during skin aging, inhibition
of the collagen-degrading MMP-1 enzyme may be critical for the prevention of skin
aging. To study the effect of maclurin on MMP-1 activity in HaCaT human keratinocyte
cells, a collagen zymography assay was performed. HaCaT human keratinocyte cells were
maintained in Dulbeco's Modified Eagle's Media (DMEM) (HyClone Laboratories, Inc,
South Logan, UT, USA) supplemented with 10% fetal bovine serum and 100 U/mL of penicillin
and 100 mg/mL streptomycin mixed antibiotics. Sodium dodecyl sulfate polyacrylamide
gel electrophoresis (SDS-PAGE) (with 0.1% collagen) was performed, and gels were washed
with zymography washing buffer (2.5% Triton X-100 in distilled water). Then, the gels
were incubated in zymography development solution (0.5 M Tris-HCl, pH 7.6, 5 mM CaCl2)
for 4 h at 37°C. The gels were stained and destained with Coomassie Brilliant Blue
R staining solution and destaining solution (20% methanol, 10% acetic acid, and 70%
distilled H2O). The unstained bands on the gel indicate collagenase activity. As shown
in Fig. 1C, the collagenase activity of MMP-1 was inhibited by maclurin, indicating
the MMP-1 suppressive effect of maclurin. A possible cytotoxic effect of a compound
may limit the opportunity for it to be further developed as a functional additive
for antiaging skin products. To investigate the cytotoxic effect of maclurin on HaCaT
human keratinocyte cells, a Cell Counting Kit-8 (CCK-8, Dojindo Molecular Technologies,
Inc., Rockville, MD, USA) assay was performed according to the manufacturer's instructions.
The cells were seeded at a density of 104 cells/well in 96-well plates with 10% fetal
bovine serum and incubated overnight. Cells were exposed to increasing concentrations
of maclurin for 24 h, and cell viability was subsequently measured. As shown in Fig. 1D,
the cytotoxicity of maclurin was not significant as indicated by the cell viability
at any dosage of maclurin. This result suggests that maclurin is not significantly
toxic to HaCaT human keratinocyte cells and may allow for this natural material to
be further modified and developed as a candidate functional agent for antiaging cosmetic
products.
To determine whether the downregulation occurs at the transcriptional level, quantitative
reverse transcription–polymerase chain reaction for MMP-1 was performed. RNA samples
from experimental cells were extracted using the RNeasy Kit (Qiagen, Hilden, Germany).
Reverse transcription for the synthesis of cDNA was executed using a cDNA Synthesis
Kit (PhileKorea Technology, Inc, Daejeon, Korea). The QuantiSpeed SYBR Kit (PhileKorea)
was used for quantitative real-time polymerase chain reaction. Primer sequences for
hMMP-1 are 5′-GAG ATCATCGGGACAACTCTCCTT-3′ (forward) and 5′-GTTGGTCCACCTTTCATCTTCAT
CA-3′ (reverse). Forty sequential cycles of denaturation (5 s at 95°C), annealing,
and extension (15 s at 60˚C) were performed. Fluorescence of SYBR Green was monitored
by the Rotor-Gene Q (Qiagen) for the determination of Ct values. The 2−
ΔΔCp method was used for the analysis of relative gene expression. As seen in Fig. 2B,
the level of MMP-1 mRNA was significantly attenuated by maclurin treatment of HaCaT
human keratinocyte cells. This may strongly indicate that the suppressive effect of
maclurin on MMP-1 in HaCaT cells is the consequence of the downregulation of the transcriptional
expression by maclurin. These results indicate that maclurin may be worth developing
as a functional agent for the prevention of skin aging. Among the various cellular
signaling pathways, mitogen-activated protein kinases and AKT signaling are well known
to be related with MMP expressions [2], [16]. Therefore, the effect of maclurin on
activation of three representative mitogen-activated protein kinases, Extracellular
signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38, was investigated
by Western blot analysis. As seen in Fig. 2B, the activation of ERK (represented by
p-ERK) was significantly downregulated by maclurin in a dosage-dependent manner. The
activation of AKT was not suppressed by maclurin as indicated by the Western blot
bands of p-AKT, which is an active form of AKT (data not shown here). It was reported
that the Activator protein 1 (AP-1) family member c-Jun and the Ets-1 transcription
factors are phosphorylated and activated by ERK [17], [18]. In addition, Nuclear factor
kappa-light-chain-enhancer of activated B cells (NF-kB) transcription factor is well
known as a major regulating factor for MMP-1 expression [19]. Among the three factors,
Ets-1 was downregulated by maclurin (Fig. 2C). These results indicate that maclurin
exerts its inhibitory effect on the transcriptional expression of MMP-1 via ERK/Ets-1
signaling.
Fig. 2
Maclurin inhibits the transcriptional expression of MMP-1 and ERK/Ets-1 signaling
in HaCaT human keratinocyte cells. (A) The mRNA level of MMP-1 was lowered by maclurin
treatment (0, 15, and 30 μM) in HaCaT human keratinocyte cells. The result was statistically
evaluated using Student t test. *p < 0.05; **p < 0.01. (B) Effect of maclurin on ERK
was investigated by Western blot analysis. Activated ERK (represented by p-ERK) was
decreased proportionally to the concentrations of applied maclurin (0, 50, and 100 μM).
(C) Cellular level of Ets-1 was downregulated by maclurin in HaCaT human keratinocyte
cells in a dosage-dependent manner. MMP, matrix metalloproteinase.
After the verification of maclurin as a potential molecule possibly used to inhibit
MMP-1 together with CK, the synergistic effect of maclurin on CK-induced inhibition
of the transcription of MMP-1 was evaluated by quantitative reverse transcription–polymerase
chain reaction (Fig. 3A). The level of MMP-1 mRNA was significantly more downregulated
when the combination of CK and maclurin was treated (15 μM of maclurin and 5 μM of
CK) than when maclurin or CK was solely treated (15 μM and 5 μM, respectively).
Fig. 3
Synergistic effect of maclurin on CK-induced inhibition of the transcriptional expression
of MMP-1 in HaCaT human keratinocyte cells. (A) The mRNA level of MMP-1 was more lowered
by the combinatorial treatment of CK and maclurin (15 μM and 5 μM, respectively) than
by the sole treatment of maclurin (15 μM) and CK (5 μM). (B) Cytotoxicity of the combination
of CK and maclurin was tested in HaCaT human keratinocyte cells. Cells were exposed
to 15 μM of maclurin, 5 μM of CK, and both maclurin/CK (15 μM and 5 μM, respectively)
for 24 h. Cell viability was assayed using the CCK-8 Kit. The results were statistically
evaluated using Student t test. *p < 0.05; **p < 0.01; ***p < 0.001;#p < 0.05; $p < 0.05).
CCK-8, Cell Counting Kit-8; CK, compound K; MMP, matrix metalloproteinase.
To test a possible cytotoxic effect of the combination of CK and maclurin, CCK-8 cell
viability assay was performed (Fig. 3B). As seen in Fig. 3B, the cytotoxic effect
of the mixture of CK and maclurin was not significant in HaCaT human keratinocyte
cells. This may open the chance for this combinatorial application to be further developed
as antiaging skin products.
In this study, we found that maclurin downregulates MMP-1 expression in HaCaT human
keratinocyte cells and induces synergistic effect on ginsenoside CK-induced inhibition
of the transcriptional expression of MMP-1. The results presented here strongly suggest
that the combination of CK and maclurin be an effective agent for skin antiaging therapies
and, therefore, may have industrial and medicinal value for application in the cosmetic
industry and the dermatologic sector.
Conflicts of interest
The author declares no conflicts of interest.