1. Introduction
Edible mushrooms are of interest for their nutritional value as well as their
pharmacological characteristics [1], such as containing low-energy indigestible
polysaccharides and having high antioxidant capacity [2]. Thus, mushroom extracts
are used to promote human health. The antioxidant properties of mushroom extracts
have been extensively studied; however, the antioxidative effects of the extracts
are thought to be attributed to tocopherols, phenolic compounds, carotenoids, and
ascorbic acid [3, 4, 5, 6, 7, 8, 9]. Mushroom polysaccharides such as -glucan are also
expected to be bioactive compounds with immunotherapeutic properties, but their
action mechanisms remain to be elucidated [10], although the presence of the
-glucan receptor is currently reported on the surface of the cell
membrane of immune cells such as macrophages and dendritic cells [11].
Basidiomycetes-X (Echigoshirayukidake) was originally discovered in
Uonuma district, Niigata prefecture, Japan as an edible mushroom [12] and found
to be a fungus strain genetically close to Ceraceomyces tessulatus.
Since the water-soluble extract of Basidiomycetes-X protects
lipopolysaccharide-induced hepatic oxidative damage in mice [13], functional
studies have been conducted as follows. Oral administration of the
aqueous extract of Basidiomycetes-X inhibits atopic dermatitis
in a mouse model [14]. Recent studies in Basidiomycetes-X have shown
potential anti-obesity functions [15, 16] and hepatoprotective functions to
prevent and ameliorate nonalcoholic steatohepatitis (NASH) in mice [17]. The dry
powder of Basidiomycetes-X is expected to contain functional ingredients
to improve fatty liver through antioxidation and inhibition of lipid peroxidation
without serious side reactions [18]. Basidiomycetes-X water extracts
exhibit high antioxidant abilities, including total phenolic content, DPPH radical scavenging activity,
Fe-reducing ability, Cu-reducing ability, and Fe-chelating
activity (Matsugo S, Sakamoto T, Nishida A, Wada N, Konishi T. Pyrrole Compound.
PCT/JP2018/043401 11/26/2018). We have previously identified pyrrole alkaloid
derivatives as candidate active components in Basidiomycetes-X [19], however, these compounds have very little antioxidant activity detected.
In the present study, we further identified antioxidant ingredients in
Basidiomycetes-X extracts assessed by their radical scavenging
activity using DPPH as a substrate. As a result, ergosterol and conjugated
linoleic acid (CLA) were found to be the major lipophilic antioxidative
components, and 2,3-dihydro-3,5-dihydroxy-6-methyl‑4H‑pyran-4-one (DDMP)
was found to be a hydrophilic antioxidative component. Moreover, pyrimidine and
purine nucleosides, including uridine and adenosine, were identified as major
components in Basidiomycetes-X water extracts.
2. Materials and Methods
2.1 Characterization of DPPH Radical Scavengers by TLC
Mycology Techno Co., Ltd. (Niigata, Japan) provided Basidiomycetes-X
dry powder as starting materials. One gram of Basidiomycetes-X dry
powder was suspended in 10 mL of the extraction solvents of water, methanol,
chloroform-methanol (1:1, v/v) and 2-propanol, respectively. These suspensions
were allowed to stand at room temperature for 4 h and mixed briefly every hour
during the extraction. Debris was removed by centrifugation at 890 g for 5 min and 10 L of the extracts were applied onto a TLC
plate with a fluorescent dye (TLC Silica gel 60 F, Merck, Darmstadt,
Germany) and developed using chloroform-methanol-acetic acid (95:5:3, v/v) as a
mobile phase. Under UV illumination at 254 nm, compounds that inhibited
fluorescence from the dye on the TLC plate were detected. After drying, the TLC
plate was immersed in 1.25 mM DPPH solution in methanol for activity staining to
detect the components showing DPPH radical scavenging activity. The band
intensity was measured using an image analysis software (ImageJ, developed by
Rasband W at NIH, Bethesda, MD).
2.2 Purification of Compound I (Ergosterol)
Five-hundred grams of Basidiomycetes-X dry powder were divided into 4
portions, and each 125 g was suspended in 500 mL of 2-propanol and stirred for 20
min using a magnetic stirrer at room temperature. The first extracts were
recovered by filtration using filter paper. Each residue on the filter paper was
suspended again in 2-propanol (400 mL). The 2-propanol extraction was repeated
four times, and in total, 4345 mL of 2-propanol extracts were recovered. The
2-propanol extracts were evaporated using a rotary evaporator, the dry matters
were dissolved in 65 mL of chloroform, and chloroform-insoluble solid was removed
by filtration using filter paper and condensed to 5 mL with a rotary evaporator.
The chloroform-soluble fraction was applied to a silica gel column (Wakogel
C-200, 75–150 m, 1.8 15 cm) and eluted with
chloroform-methanol-acetic acid (95:5:3, v/v) as a developing solvent. The elute
was recovered and the solvent was changed to 2 mL of chloroform after evaporation
with a rotary evaporator. The chloroform-soluble fraction was applied to an
alumina column (Wako active alumina, 200–300 mesh, 1.8 15 cm) and
eluted with chloroform as a developing solvent. The chloroform elute was
recovered and the solvent was changed to 2 mL of hexane-ethyl acetate (8:2, v/v).
The insoluble solid was removed by filtration through a 0.45-m PTFE
syringe filter (RJF1345NH, Rephile), and the hexane-ethyl acetate soluble
fraction was further purified using an HPLC system with a normal phase column
(Wakopak Wakosil 10 SIL, 4.0 300 mm). The mobile phase was
hexane-ethyl acetate (8:2, v/v) at a flow rate of 0.6 mL min. The
ergosterol-containing fraction showing a characteristic UV absorption spectrum
with four peaks at 263, 272, 282 and 293 nm was recovered. The final product of
ergosterol (4.5 mg) was dissolved in chloroform (Supplementary Table 1).
The amount of ergosterol was spectrophotometrically determined using an
absorption coefficient of 0.97 10 L mol cm at
262 nm [20].
2.3 Measurement of Ergosterol Content by HPLC
One gram of Basidiomycetes-X dry powder was suspended in 4 mL of
methanol and stirred for 20 min using a magnetic stirrer at room temperature. The
methanol-insoluble solid was removed by filtration through filter paper. The
filtrate was collected and the residue on the filter paper was once again
resuspended in 3.2 mL of methanol. The methanol extraction was repeated three
times. Debris was removed by filtration through a 0.45-m PTFE syringe
filter and the ergosterol-containing methanol extract (20 L) was analyzed
using an HPLC system with a pump (PU-2087 Plus Intelligent Prep. Pump, JASCO)
equipped with a reversed-phase column (Cosmosil 5C18-MS, 4.6 150 mm,
Nacalai). The mobile phase was 100% methanol at a flow rate of 0.6 mL
min for isocratic elution. The UV spectrum was recorded with a JASCO
photodiode array detector detector (MD-2018 Plus). A was traced to draw a
chromatogram and ergosterol was identified by its UV absorption spectrum with
characteristic four peaks at 263, 272, 282 and 293 nm. The amount of ergosterol
was determined from a standard curve constructed with known amounts (20 to 80 ng)
of the authentic ergosterol standard (Tokyo Chemical Industry Co., Ltd.).
2.4 Purification of Compound II (CLA)
Basidiomycetes-X powder (500 g) was used as the starting material, and
2-propanol extracts were prepared as described in the purification of ergosterol
section above. The 2-propanol extracts were evaporated using a rotary evaporator,
and the dry matters (2.4 g) were dissolved in 100 mL of chloroform.
Chloroform-insoluble materials were removed by filtration using filter paper,
after which the filtrate was evaporated using a rotary evaporator, leading to the
recovery of 1.4 g of chloroform-soluble materials. After dissolving in
chloroform, the chloroform-soluble sample was applied to a silica gel column
(Wakogel C-200, 75–150 m, 1.8 15 cm) and eluted with
chloroform-methanol-acetic acid (95:5:3, v/v). The unabsorbed fraction was
collected, evaporated (977 mg) and dissolved in chloroform (2 mL). The chloroform
solution was applied to an alumina column (Wako active alumina, 200–300 mesh,
1.8 15 cm), washed with 100% chloroform and eluted with
chloroform-methanol-acetic acid (95:5:3, v/v). The elute was collected,
evaporated (225 mg) and dissolved in hexane-ethyl acetate-acetic acid (60:40:1,
v/v, 2 mL). The sample (2 mL) was applied to a silica gel column (Wakogel C-200,
75–150 m, 1.8 15 cm) and eluted with hexane-ethyl
acetate-acetic acid (60:40:1, v/v). The fractions showing the characteristic UV
absorption spectrum with an absorption maximum at 233 nm were collected,
evaporated (151 mg) and dissolved in chloroform (0.5 mL). After adjusting the
solvent to methanol-chloroform-water (90:5:5, v/v), the sample was filtered
through a 0.45-m PTFE syringe filter (RJF1345NH, Rephile) and then
purified using an HPLC system with a reversed-phase column (CAPCELL PAK C18 AQ
S5, 10 250 mm, Shiseido). The mobile phase was 90% (v/v) methanol
with 0.1% (v/v) acetic acid at a flow rate of 3.0 mL min. A was
monitored to detect the target compound. The peak fraction at 25 min was
collected, evaporated (29 mg) and dissolved in chloroform-methanol (3:40, v/v).
After filtration through a 0.45-m PTFE syringe filter (RJF1345NH,
Rephile), the filtrate was further purified using the same HPLC system with a
reversed-phase column (CAPCELL PAK C18 AQ S5, 10 250 mm, Shiseido). In
the second chromatography, the mobile phase was 85% (v/v) methanol with 0.1%
(v/v) acetic acid at a flow rate of 3.0 mL min. A was monitored
to detect compound II. The peak fraction at 61 min was collected, evaporated and
dissolved in chloroform as the final product (11.4 mg) (Supplementary
Table 2). Purified compound II was used for HPLC analysis and MS analysis.
Because the purified CLA was degraded during storage at 4 C for 2–3
months, CLA was purified again from Basidiomycetes-X dry powder (100 g)
to obtain enough quantity and quality sample for the NMR analysis.
Basidiomycetes-X dry powder was suspended in a mixed solvent containing
chloroform (250 mL), methanol (500 mL), and acetic acid (0.1 N, 200 mL) and
stirred for 2 h at room temperature. The insoluble solid was filtered off, and
chloroform (250 mL) and acetic acid (0.1 N, 250 mL) was added to the filtrate.
This solution was shaken in a separatory funnel and separated into two phases.
The lower layer was collected, and the organic solvents were removed by
evaporation under vacuum. The dissolved part in ethyl acetate-hexane (2:8, v/v)
was passed through a SNAP ultra 10 g HP-Sphere column (Biotage Isolea one,
gradient elution by hexane and ethyl acetate). The fractions eluting before
ergosterol were collected and dried in vacuo. The crude CLA
(approximately 170 mg) was dissolved in 10 mL of methanol-chloroform-water
(90:5:5, v/v) and further purified by reversed-phase HPLC. Debris was removed by
filtration through a 0.45-m PTFE syringe filter (RJF1345NH, Rephile) and
the filtrate was purified using an HPLC system with a reversed-phase column
(Inertsustain, 5 m, 14 150 mm, GL Sciences). The mobile phase
was 87.5% (v/v) methanol with 0.1% (v/v) acetic acid at a flow rate of 5.5 mL
min. A was monitored to detect CLA. The peak fraction at 20 min
was collected, evaporated (39 mg) and dissolved in 4.3 mL of methanol-chloroform
(3:40, v/v). Debris was removed by filtration through a 0.45-m PTFE
syringe filter (RJF1345NH, Rephile), the filtrate was purified using an HPLC
system with a reversed-phase column (CAPCELL PAK C18 AQ S5, 10 250 mm,
Shiseido) again. In the second chromatography, the mobile phase was 85% (v/v)
methanol with 0.1% (v/v) acetic acid at a flow rate of 3.0 mL min.
A was monitored to detect CLA. The peak fraction at 43 min was collected,
evaporated and dissolved in chloroform as the final product (11 mg). The purified
CLA was used for the NMR analysis.
2.5 Measurement of CLA Content by HPLC
One gram of Basidiomycetes-X dry powder was suspended in 10 mL of
methanol, and stirred for 24 h using a magnetic stirrer at room temperature.
Debris was removed by filtration through filter paper and a 0.45-m PTFE
syringe filter (RJF1345NH, Rephile). The CLA-containing methanol extract (20
L) was analyzed using an HPLC system with a pump (PU-2087 Plus Intelligent
Prep. Pump, JASCO) equipped with a reversed-phase column (Cosmosil 5C18-MS, 4.6
150 mm, Nacalai). The mobile phase was 90% (v/v) methanol with 0.1%
(v/v) acetic acid at a flow rate of 0.6 mL min for isocratic elution. The
UV spectrum was recorded with a JASCO photodiode array detector (MD-2018 Plus).
A was traced to draw a chromatogram. CLA was identified by its
characteristic UV absorption spectrum with an absorption maximum at 232 nm.
The authentic standards trans-10,cis-12-octadecadienoic acid
(10(E),12(Z)-CLA) and cis-9,trans-11-octadecadienoic acid
(9(Z),11(E)-CLA) were purchased from Cayman Chemical Company (Ann Arbor, MI
48108, USA). The concentration of 10(E),12(Z)-CLA in ethanol was
spectrophotometrically determined using an absorption coefficient of 28,700 L
mol cm at 232 nm [21], and 140.8 ng of 10(E),12(Z)-CLA was
injected into the HPLC system as an external standand.
2.6 HPLC Analysis of Basidiomycetes-X Water Extract
Basidiomycetes-X dry powder (50 g) was suspended in water (500 mL) and
stirred for 24 h using a magnetic stirrer at room temperature. After filtration
through filter paper under reduced pressure, debris was additionally removed by
filtration through a 0.45-m PTFE syringe filter (RJF1345NH, Rephile). The
water extract was analyzed using an HPLC system equipped with a reversed-phase
column (Cosmosil 5C18-MS, 4.6 150 mm, 5 m, Nacalai). The mobile
phase was changed for linear gradient elution using a pump (PU-2087 Plus
Intelligent Prep. Pump, JASCO). During the initial 5 min, 0.1% (v/v) acetic acid
was eluted, and the methanol concentration in the eluent increased linearly up to
99.9% (v/v) methanol with 0.1% (v/v) acetic acid over 95 min. After a 10-min
elution of 99.9% (v/v) methanol with 0.1% (v/v) acetic acid, the methanol
concentration in the eluent decreased linearly to 0% (v/v) methanol with 0.1%
(v/v) acetic acid over 5 min and stabilized at 0.1% (v/v) acetic acid for 10
min. The flow rate was maintained at 0.6 mL min during the elution. The
UV spectrum was recorded with a JASCO photodiode array detector (MD-2018 Plus).
2.7 Detection of DPPH Radical Scavengers in Water Extract
One gram of Basidiomycetes-X dry powder was suspended in 10 mL of water
and stirred for 2 h using a magnetic stirrer at room temperature. Debris was
removed by centrifugation at 22,200 g for 5 min, filtration
through filter paper and subsequent filtration through a 0.45-m PTFE
syringe filter (RJF3245NH, Rephile). The water extact was frationated using a
preparative HPLC system equipped with a reversed-phase column (CAPCELL PAK C18 AQ
S5, 10 250 mm, Shiseido). The mobile phase changed stepwise from 7.5%
(v/v) methanol with 0.1% (v/v) acetic acid during the first 30 min, to 20%
(v/v) methanol with 0.1% (v/v) acetic acid during the next 40 min, to 40% (v/v)
methanol with 0.1% (v/v) acetic acid during the next 20 min, and to 99.9% (v/v)
methanol with 0.1% (v/v) acetic acid during the final 15 min. The flow rate was
kept at 3.0 mL min during elution with a pump (PU-2087 Plus, JASCO).
A was recorded with a JASCO UV/VIS detector (UV-2075 Plus). Twelve peak
fractions detected with absorption at 260 nm and 7 interval fractions without
absorption at 260 nm were collected, and condensed using a rotary evaporator or a
lyophilizer. Each condensed fraction was dissolved in 10 L of methanol and
spotted onto a TLC plate (TLC Silica gel 60 F, Merck). After separation
using hexane-ethyl acetate (4:1, v/v) as a developing solvent, the plate was
dried at room temperature for 20 min. A 375 M DPPH solution in methanol
was sprayed evenly on the plate and DPPH radical scavengers were detected. The
spot intensity detected by activity staining was measured using an image analysis
software (ImageJ, developed by Rasband W at NIH, Bethesda, MD).
2.8 Purification of Compound III (DDMP)
Seventy grams of Basidiomycetes-X dry powder were divided into 7
portions, and each 10 g was suspended in 100 mL of methanol and stirred for 24 h
using a magnetic stirrer at room temperature. Debris was removed by filtration
through filter paper, the methanol extract was evaporated with a rotary
evaporator, after which the dry materials (12.8 g) were dissolved in 140 mL of
water. The water-insoluble solid was removed by filtration through filter paper.
The filtrate was divided into 7 portions, and methanol (20 mL) and chloroform (20
mL) were added to the filtrate (20 mL). After mixing vigorously using a 100-mL
separatory funnel and separated into two phases, the upper aqueous phase was
collected. After evaporation with a rotary evaporator, the dry materials were
dissolved in 93 mL of water. Debris was removed by filtration through a
0.45-m PTFE syringe filter (RJF1345NH, Rephile). The DDMP-containing
aqueous fraction was purified using an HPLC system equipped with a reversed-phase
column (CAPCELL PAK C18 AQ S5, 10 250 mm, Shiseido). The mobile phase
was 0.1% (v/v) acetic acid at a flow rate of 3.0 mL min for isocratic
elution. A was monitored to detect the target compound and the peak
fraction at 30 min was recovered. After removal of the solvent, 178 mg of dry
material was dissolved in 2 mL of water and filtered through a 0.45-m PTFE
syringe filter (RJF1345NH, Rephile). The filtate was additionally purified by the
second chromatographic preparation using a reversed-phase column (CAPCELL PAK C18
AQ S5, 10 250 mm, Shiseido). The mobile phase was 0.1% (v/v) acetic
acid at a flow rate of 3.0 mL min for isocratic elution. A was
monitored to detect compound III and the peak fraction at 30 min was recovered.
After removal of the solvent, 13.4 mg of dry material was obtained as the final
product.
2.9 Measurement of DDMP Content by HPLC
One gram of Basidiomycetes-X dry powder was suspended in 10 mL of
methanol and stirred for 24 h using a magnetic stirrer at room temperature. The
methanol-insoluble solid was removed by filtration through filter paper. Debris
was additionally removed by centrifugation at 21,000 g for 2
min and subsequent filtration through a 0.45-m PTFE syringe filter
(RJF1345NH, Rephile). The methanol extract (20 L) was analyzed using an
HPLC system with a pump (PU-2087 Plus Intelligent Prep. Pump, JASCO) equipped
with a reversed-phase column (Cosmosil 5C18-MS, 4.6 150 mm, Nacalai).
The mobile phase was 0.1% (v/v) acetic acid for the initial 5 min and changed
linearly up to 99.9% (v/v) methanol with 0.1% (v/v) acetic acid over 95 min for
gradient elution. The flow rate was constant at 0.6 mL min. The UV
absorption spectrum was recorded with a JASCO photodiode array detector (MD-2018
Plus) and A was traced to draw a chromatogram. A known amount of purified
DDMP (400 ng) was used as the external standard.
2.10 Purification of Compound IV (Uridine) and Compound V
(Adenosine)
Basidiomycetes-X dry powder (100 g) was added to 800 mL of
water and stirred for 12 h using a magnetic stirrer at room temperature. The
water-insoluble solid was removed by centrifugation at 2000 g
for 3 min and subsequent filtration through filter paper to obtain clear aqueous
extract. The extraction using distilled water was repeated 4 times, and 2010 mL
of the water extract was collected in total. The water extract was condensed
using a rotary evaporator, and the resulting dry materials (64.85 g) were
dissolved in 450 mL of methanol. The methanol-insoluble solid was removed by
filtration through filter paper and the filtrate was condensed to 100 mL using a
rotary evaporator. Equal volumes of water and chloroform were added to the 100-mL
condensed methanol soluble fraction, mixed vigorously using a 500-mL separatory
funnel, and waited to separate into two phases. The lower organic phase was
removed. The chloroform extraction was repeated 3 times and the clear aqueous
phase (125 mL) was collected. The aqueous phase was recovered and condensed using
a rotary evaporator, and the resulting dry materials were dissolved in 50 mL of
methanol. The methanol-soluble fraction was maintained at –30 C for 12
h and the precipitate was removed by filtration through filter paper. After
evaporation by a rotary evaporator, the dry materials (10.85 g) were dissolved in
25 mL of water and debris was removed by filtration through a syringe filter
(0.45 m, RJF1345NH, Rephile). The filtrate was passed through a
reversed-phase column (Cosmosil 5C18-MS-II, 4.6 150 mm, Nacalai) to
remove the substances adsorbed to the column. The mobile phase was 15% (v/v)
methanol with 0.1% (v/v) acetic acid at a flow rate of 1.0 mL min. The
elution of the target compound was monitored by A, and the fraction at
retention times of 0–30 min was collected as fraction 1. The solvent of fraction
1 was removed using a rotary evaporator and the resulting materials were
dissolved in 20 mL of water. After filtration through a syringe filter (0.45
m, RJF1345NH, Rephile), the sample was purified using a preparative HPLC
system equipped with a reversed-phase column (CAPCELL PAK C18 AQ S5, 10
250 mm, Shiseido). The mobile phase was 7.5% (v/v) methanol with
0.1% (v/v) acetic acid at a flow rate of 3.0 mL min. The elution of the
target compound was monitored by A. The fraction at retention times
of 8.87–10.99 min was collected as fraction 2, and the fraction at retention
times of 22.6–25.9 min was collected as compound V.
Fraction 2 was condensed using a rotary evaporator and the resulting materials
were dissolved in 10 mL of water. After filtration through a syringe filter (0.45
m, RJF1345NH, Rephile), the water-soluble fraction was further
purified using another HPLC system equipped with a reversed-phase column
(Inertsil ODS-3, 4.6 150 nm, 5 m, GL Sciences). The mobile
phase was 0.1% (v/v) acetic acid at a flow rate of 1.0 mL min. The
elution of the target compound was monitored by A, and the fraction at
retention times of 16.5–19.5 min was collected as compound IV. Compound IV (10.6 mg, Supplementary Table 3) and compound V (14.0 mg, Supplementary Table 4) were obtained after the removal of the solvent with a lyophilizer.
2.11 Measurement of Uridine Content by HPLC
One gram of Basidiomycetes-X dry powder was suspended in 20 mL
of water and stirred for 2 h using a magnetic stirrer at room temperature. Debris
was removed by centrigugation at 22,200 g for 2 min and the
supernatant was diluted by the addition of a 3-fold volume of water to obtain a
12.5 mg mL Basidiomycetes-X water extract. After filtration
through a syringe filter (0.45 m, RJF1345NH, Rephile), the water extract
(20 L) was analyzed using an HPLC system with a pump (PU-2087 Plus
Intelligent Prep. Pump, JASCO) equipped with a reversed-phase column (Inertsil
ODS-3, 4.6 150 nm, 5 m, GL Sciences). The mobile phase was
7.5% (v/v) methanol with 0.1% acetic acid at a flow rate of 0.6 mL min
for isocratic elution. The UV absorption spectrum was recorded with a JASCO
photodiode array detector (MD-2018 Plus), and A was traced to draw a
chromatogram. The amount of uridine was determined from a standard curve
constructed with known amounts (60 to 400 ng) of the authentic standard uridine,
which was purchased from Sigma–Aldrich. The concentration of the uridine
standard solution was determined using the absorption coefficient of uridine
(10,100 L mol cm at 262 nm).
2.12 Measurement of Adenosine Content by HPLC
One gram of Basidiomycetes-X dry powde was suspended in 20 mL
of water and stirred for 2 h using a magnetic stirrer at room temperature. Debris
was removed by centrigugation at 22,200 g for 2 min and the
supernatant was diluted by the addition of an equal volume of water to obtain 25
mg mL Basidiomycetes-X water extract. After filtration
through a syringe filter (0.45 m, RJF1345NH, Rephile), the water extact
(20 L) was analyzed using an HPLC system with a pump (PU-2087 Plus
Intelligent Prep. Pump, JASCO) equipped with a reversed-phase column (Inertsil
ODS-3, 4.6 150 nm, 5 m, GL Sciences). The mobile phase was 15%
(v/v) methanol with 0.1% (v/v) acetic acid at a flow rate of 0.6 mL min
for isocratic elution. The UV absorption spectrum was recorded with a JASCO
photodiode array detector (MD-2018 Plus), and A was traced to draw a
chromatogram. The amount of adenosine was determined from a standard curve
constructed with known amounts (66 to 435 ng) of the authentic standard
adenosine, which was purchased from Sigma–Aldrich. The concentration of the
adenosine standard solution was determined using the absorption coefficient of
adenosine (14,900 L mol cm at 260 nm).
2.13 MS Analysis
EI-MS and EI HR-MS analyses were performed at the Research Institute for
Instrumental Analysis at Kanazawa University using a mass spectrometer (JMS-700;
JEOL Ltd., Tokyo). FAB-MS and FAB HR-MS analyses were performed using the JEOL
JMS-700 mass spectrometer with glycerol or YOKUDEL-FAB-Matrix (JEOL) as a matrix.
2.14 Spectroscopic Analysis
The UV absorption spectra were recorded with a Hitach spectrophotometer
(U-3900). During HPLC analyses, the UV/VIS spectra were recorded with a JASCO
photodiode array detector (MD-2018 Plus). NMR analyses were performed using JEOL
NMR spectrometers (ECA600 or ECS400) with 3-(trimethylsilyl)-1-propanesulfonic
acid-d6 sodium salt (TMP) as an internal standard to determine 0 ppm.
3. Results
3.1 Characterization of Lipophilic Antioxidants in
Basidiomycetes-X
Fig. 1. shows the TLC separation of DPPH radical scavengers in the
Basidiomycetes-X extracts using different extraction solvents.
Almost all of the water-soluble DPPH radical scavengers were retained at the
origin under the conditions that we used for TLC separation (Fig. 1B, Lane 1).
Compounds with DPPH radical scavenging activities at Rf 0.89 and Rf 0.86 were
detected in the methanolic extract (Fig. 1B, Lane 2), and their relative
intensities were 6.2% (Rf 0.89) and 21% (Rf 0.86), respectively, although
approximately 55% of the DPPH radical scavengers were retained at the origin
(Fig. 1B, Lane 2). The bands at Rf 0.89 and Rf 0.86 were specifically detected in
the 2-propanol extract (Fig. 1B, Lane 4). The lipophilic DPPH radical scavengers
in Basidiomycetes-X can be extracted using 2-propanol and
separated by column chromatography. Thus, we focused on compound I at Rf 0.89 and
compound II at Rf 0.86 and characterized them further.
Fig. 1.
Detection of DPPH radical scavengers in
Basidiomycetes-X extracts after separation by TLC. Basidiomycetes-X extracts were prepared using water (Lane 1), methanol
(Lane 2), chloroform-methanol (1:1, v/v) (Lane 3) and 2-propanol (Lane 4). After
centrifugation, 10 L of the extracts were applied to TLC plates (Silica
gel 60 F, Merck) and separated using chloroform-methanol-acetic acid
(95:5:3, v/v) as a mobile phase. UV-absorbing compounds that inhibited
fluorescence from a dye on the TLC plate were detected under UV illumination at
254 nm (Panel A). DPPH radical scavengers on the plate were detected by staining
with 1.25 mM DPPH solution in methanol (Panel B). The positions of ergosterol
(I), CLA (II) and DDMP (III) are indicated.
3.2 Identification of Ergosterol
As described above (section 2.2), 4.5 mg of compound I at Rf 0.89 was obtained
from 500 g of Basidiomycetes-X dry powder (Supplementary Table
1). Purified compound I showed a characteristic UV absorption spectrum with four
absorption peaks at 263, 272, 282 and 293 nm (Fig. 2D), and a molecular ion with
a m/z of 397 was detected by EI-MS analysis. These features were identical to
those of ergosterol. Compound I eluted identically to the commercially available
ergosterol standard when analyzed using our HPLC system (data not shown).
Supplementary Table 5 displays the NMR spectroscopic data of compound I
to compare with the ergosterol standard. The C and H NMR signals
were essentially identical to each other (Supplementary Table 5, Ref.
[22]). Taken together, these results identified compound I at Rf 0.89 with DPPH
radical scavenging activity as ergosterol. The ergosterol content in the
Basidiomycetes-X powder was measured by methanol extraction and
the following HPLC analysis. Its content (167 g g) was similar to
a previous report of ergosterol contents in edible mushrooms [23]. The calculated
recovery was 5.4% of compound I during our preparation starting from 500 g of
the dry powder.
Fig. 2.
HPLC analysis of compound I (ergosterol) from
Basidiomycetes-X. The methanol extract (A, C) and the purified
ergosterol (B, D) were analyzed by an HPLC system equipped with a reversed-phase
column (Cosmosil 5C-18-MS, 4.6 150 mm, Nacalai) using 100% methanol
as the mobile phase at a flow rate of 0.6 mL min for isocratic elution
using a pump (PU-2087 Plus Intelligent Prep. Pump, JASCO). Chromatograms detected
by A of the methanol extract (A) and purified ergosterol (B). The UV
absorption spectrum was recorded with a JASCO photodiode array etector (MD-2018
Plus). Absorption spectra at 14.2 min of the methanol extract (C) and at 16.2 min
of purified ergosterol (D).
3.3 Identification of CLA
As described above (section 2.4), 11.4 mg of compound II at Rf 0.86 was obtained
from 500 g of Basidiomycetes-X powder (Supplementary Table 2).
Purified compound II displayed a characteristic UV absorption spectrum with a
single absorption maximum at 233 nm (Fig. 3D), and the strong UV absorption at
233 nm suggests a conjugated double bond in the acyl group, which is a
characteristic feature of a conjugated linoleic acid (CLA) [21]. The molecular
ion with a m/z 280 was detected by both FAB-MS and EI-MS analyses. A m/z 280.2401
detected by FAB HR-MS analysis of compond II indicates the molecular formula of
CHO with errors of +0.8 ppm and –0.1 mmu. Purified compound
II eluted at identical retention times to the CLA standards
trans-10,cis-12-octadecadienoic acid and
cis-9,trans-11-octadecadienoic acid when analyzed using our
HPLC system (data not shown). To identify the isomer of CLA, NMR analysis was
performed. Supplementary Table 6 displays the NMR spectroscopic data of
compound II, and these signals were identical or highly similar to those of
trans-10,cis-12-octadecadienoic acid. These results identified
compound II at Rf 0.86 with high DPPH radical scavenging activity as
trans-10,cis-12-octadecadienoic acid (10(E),12(Z)-CLA). The CLA
content in the Basidiomycetes-X powder was measured by methanol
extraction and the following HPLC analysis. Its content (198 g g)
was similar to that of ergosterol (167 g g), consistent with the
HPLC analysis result of the 2-propanol extract in which ergosterol and CLA were
detected as the main components (data not shown). The calculated recovery was
11.5% of compound II during our preparation starting from 500 g of the dry
powder.
Fig. 3.
HPLC analysis of purified compound II (CLA) from
Basidiomycetes-X. The 2-propanol extract (A,C) and purified compound
II (B,D) were analyzed by an HPLC system equipped with a reversed-phase column
(Cosmosil 5C-18-MS, 4.6 150 mm, Nacalai) using 90% methanol with
0.1% acetic acid as the mobile phase at a flow rate of 0.6 mL min for
isocratic elution using a pump (PU-2087 Plus Intelligent Prep. Pump, JASCO).
Chromatograms detected by A of the 2-propanol extract (A) and purified
compound II (B). The UV absorption spectrum was recorded with a JASCO photodiode
array detector (MD-2018 Plus). Absorption spectra at 15.7 min of the 2-propanol
extract (C) and at 17.7 min of the purified CLA (D). Ergosterol eluted at 9.5 min
after changing the developing solvent to 100% methanol. Thus, it is not included
in the chromatogram of panel A.
3.4 Characterization of Water-Soluble Antioxidants in
Basidiomycetes-X
In the Basidiomycetes-X water extract, DPPH radical scavengers
that stayed at the origin were detected (Fig. 1, Lane 1), which suggests the
presence of hydrophilic components of antioxidants in Basidiomycetes-X. Thus, the water extract was characterized to seek
water-soluble antioxidants as described above (section 2.6). Fig. 4 shows a
chromatogram of the Basidiomycetes-X water extract analyzed
using an analytical HPLC system. Six prominent peaks were detected by monitoring
the UV absorbance at 260 nm, two of which were expected to be pyrrole alkaloid
derivatives according to their UV absorption spectra and retention times (Fig. 4,
Table 1, Ref. [19]).
Fig. 4.
HPLC analysis of a water-soluble extract from
Basidiomycetes-X. A chromatogram detected by A (A) and UV-VIS
spectra of peak 1 (B), peak 2 (C), peak 3 (D), peak 4 (E) and peak 5 (F) are
shown. The extract from Basidiomycetes-X was separated by an HPLC system
with a reversed-phase column (Cosmosil 5C18-MS, 4.6 150 mm, Nacalai)
and eluted by gradient elution as described (section 2.6).
Table 1.Summary of water-soluble compounds identified in
Basidiomycetes-X.
Peak no. |
Retention time (min) |
Absorption maximum and shoulder (nm) |
Compound |
Reference |
1 |
14.5 |
262 |
Uridine |
This study |
2 |
16.2 |
297 |
2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP) |
This study |
3 |
21.2 |
260 |
Adenosine |
This study |
4 |
30.2 |
297 (260) |
4-[2-formyl-5-(hydroxymethyl)-1H-pyrrole-1-yl] butanamide |
[19] |
5 |
36.8 |
297 (260) |
4-[2-formyl-5-(hydroxymethyl)-1H-pyrrol-1-yl] butanoic acid |
[19] |
Water-soluble compounds with UV absorption were analyzed by our HPLC system as
described (section 2.6). The chromatogram and the UV absorption spectra are shown
in Fig. 4. |
The separation of DPPH radical scavenging activities in
Basidiomycetes-X water extract using preparative HPLC was performed as
described above (section 2.7), and the fraction containing a compound with a UV
absorption maximum at 297 nm showed approximately 17% of the total DPPH radical
scavenging activity separated by the HPLC system. When analyzed using an
analytical HPLC system, the compound with an absorbance maximum at 297 nm with
DPPH radical scavenging activity was identical to peak 2, which is shown in Fig. 4. Thus, the compound, named compound III, was purified and identified as a
water-soluble antioxidant in Basidiomycetes-X. Moreover, peaks 1 and 3,
which are shown in Fig. 4, were further characterized as the main components,
compound IV and compound V, respectively, in the water extract of
Basidiomycetes-X.
3.5 Identification of DDMP
As described above (section 2.8), compound III (13.4 mg) was obtained from
Basidiomycetes-X dry powder (70 g). Purified compound III displayed a
characteristic UV absorption spectrum with a single absorption maximum at 296 nm
(data not shown). A m/z of 144.0433 detected by EI HR-MS analysis of compound III
indicates the molecular formula of CHO with errors of +7.2 ppm
and +1.0 mmu. Supplementary Table 7 displays the NMR spectroscopic data
of compound III, and these signals were identical or highly similar to those of
2,3-dihydro-3,5-dihydroxy-6-methyl‑4H‑pyran-4-one (DDMP) [24]. Taken
together, these results identified compound III with DPPH radical scavenging
activity as DDMP (Fig. 5). The DDMP content in the
Basidiomycetes-X powder was measured by methanol extraction and
the following HPLC analysis. Its content of approximately 3500 g g suggests a calculated recovery of 5.5% of compound III during our preparation
starting from 70 g of the dry powder.
Fig. 5.
Structure of compound III (DDMP) purified from
Basidiomycetes-X.
3.6 Identification of Uridine
Compound IV was purified from 100 g of Basidiomycetes-X powder
as described above (section 2.10), and 10.6 mg of the final product was obtained
(Supplementary Table 3). The HPLC chromatogram of purified compound IV
and its UV absorption spectrum with a characteristic absorption maximum at 262 nm
were identical to those of the uridine standard (data not shown). FAB-MS analysis
of purified compound IV showed molecular ion fragments with m/z 245 and m/z 113,
which were thought to be uridine and uracil, respectively. A m/z of 245.0783
detected by FAB HR-MS analysis of compound IV indicates the molecular formula of
CHNO with errors of +3.8 ppm and +0.9 mmu.
Supplementary Table 8 displays the NMR spectroscopic data of compound IV
to compare with the uridine data. The C and H NMR signals were
essentially identical to one another. Taken together, these results identified
compound IV as uridine. The uridine content in the
Basidiomycetes-X powder was measured by water extraction and
the following HPLC analysis. Its content of approximately 769 g g
suggests a calculated recovery of 14% of compound IV during our preparation
starting from 100 g of the dry powder. The level of uridine in the
Basidiomycetes-X powder was similar to the content in the
enzymatically hydrolyzed extracts of the edible Korean mushrooms
Pleurotus ostreatus, Agaricus bisporus and Flammulina
velutipes [25].
3.7 Identification of Adenosine
Compound V was purified from 100 g of Basidiomycetes-X powder
as described above (section 2.10), and 14.0 mg of the final product was obtained
(Supplementary Table 4). The HPLC chromatogram of purified compound V
and its UV absorption spectrum with a characteristic absorption maximum at 260 nm
were identical to those of the adenosine standard (data not shown). FAB-MS
analysis of purified compound V showed molecular ion fragments with m/z 268 and
m/z 136, which were thought to be adenosine and adenine, respectively. A m/z of
268.1037 detected by FAB HR-MS analysis of compound V indicates the molecular
formula of CHNO with errors of –3.3 ppm and –0.9 mmu.
Supplementary Table 9 displays the NMR spectroscopic data of compound V
to compare with the adenosine data. The C and H NMR signals were
essentially identical to each other. Taken together, these results identified
compound V as adenosine. The adenosine content in the
Basidiomycetes-X powder was measured by water extraction and
the following HPLC analysis. Its content of approximately 424 g g suggests a calculated recovery of 33% of compound V during our preparation
starting from 100 g of the dry powder. The level of adenosine in the
Basidiomycetes-X powder was similar to the content in the
Chinese medicinal mushroom DongChongXiaCao, Cordyceps sp. [26].
4. Discussion
Basidiomycetes-X (Echigoshirayukidake) is a local speciality mushroom
in Niigata prefecture in Japan, which has been distributed as a precious cuisine
material or as a resource for functional food and medicine. Thus far, several
beneficial health functions, such as potential antioxidant-inflammation
activities, anti-obesity function, prevention of lipidemia, liver fat
accumulation, atopic inflammation, and amelioration of NASH, have been reported
(for a review, [12]). In this study, antioxidative compounds, including
ergosterol, conjugated linoleic acid (CLA) and
2,3-dihydro-3,5-dihydroxy-6-methyl‑4H‑pyran-4-one (DDMP), were
identified in Basidiomycetes-X. Ergosterol and CLA were relatively
hydrophobic, and thus, 2-propanol was used as the suitable extraction solvent
(Fig. 1). DDMP is a hydrophilic radical scavenger that is water-soluble and
unable to separate using normal-phase chromatography (Fig. 1). The DPPH radical
scavengers retained at the origin (Fig. 1) were expected to be hydrophilic
radical scavengers in water-soluble extracts, and we identified DDMP as one of
the major water-soluble radical scavengers. Uridine and adenosine were detected
as major components in the water extract comparable to DDMP by reversed-phase
HPLC (Fig. 4). Table 2 summarizes the contents of ergosterol, (10E, 12Z)-CLA,
DDMP, uridine and adenosine, which were identified in Basidiomycetes-X
powder in this study. Pyrrole alkaloid derivatives have been reported as other
candidate active components in Basidiomycetes-X (Fig. 4, Tables 1,2, Ref. [19]). These compounds are expected to be involved in the reported
pharmacological functions of Basidiomycetes-X [12], and the
function of each compound will be elucidated in future studies.
Table 2.Contents of the Identified Compounds in
Basidiomycetes-X.
Compound |
Content |
Reference |
g g |
Ergosterol |
167 14 |
This study |
(10E, 12Z)-CLA |
198 6 |
This study |
DDMP |
3500 16 |
This study |
Uridine |
769 54 |
This study |
Adenosine |
424 39 |
This study |
Pyrrole alkaloid I |
825 39 |
[19] |
Pyrrole alkaloid II |
484 23 |
[19] |
Each value indicates the average standard deviation (N = 3). The contents of ergosterol, (10E, 12Z)-CLA, DDMP, uridine and adenosine in Basidiomycetes-X dry powder were measured as described (section 2.3,
2.5, 2.9, 2.11 and 2.12). 4-[2-formyl-5-(hydroxymethyl)-1H-pyrrol-1-yl] butanoic acid,
peak 5 shown in Fig. 4. 4-[2-formyl-5-(hydroxymethyl)-1H-pyrrole-1-yl] butanamide, peak
4 shown in Fig. 4. |
Ergosterol is provitamin D2, which converts to biologically active vitamin D2 by
exposure to UV light [27]. It is also known as the main sterol in the cell
membrane of fungi [23, 28]. It has been reported that ergosterol contents are
positively correlated with antioxidant activities in button mushrooms [29]. In
Basidiomycetes-X extracts, ergosterol significantly contributed
to the total antioxidant capacity (Fig. 1). Ergosterol acts as an
anti-inflammatory substance in lipopolysaccharide-stimulated macrophages
in vitro [28]. Fungal ergosterol is a direct trigger of macrophage
pyroptosis, which is a form of inflammatory programmed cell death [30, 31].
Moreover, ergosterol from Agaricus blazei, a commercially cultivated
mushroom, is identified as an antitumor compound [32], and ergosterol is the main
anticancer ingredient in the medicinal mushroom Amauroderma rude [22].
Conjugated linoleic acid (CLA) is a C fatty acid with conjugated double
bonds in the acyl group, and positional and stereo isomers of CLA are known. CLA
is contained in beef and milk, and its health benefits are of interest as a
dietary supplement. Numerous physiological properties of CLA, including
antiadipogenic, antidiabetogenic, anticarcinogenic, and antiatherosclerotic
effects, have been reported [33, 34], and it acts as a DPPH radical scavenger
in vitro [35]. CLA accounts for approximately 1% of the total fatty
acids in ruminant milk, and cis-9,trans-11-octadecadienoic acid
(9(Z),11(E)-CLA), which is named rumenic acid, is the most abundant CLA isomer
[33, 34]. 10(E),12(Z)-CLA was identified in Basidiomycetes-X extracts,
and approximately 21% of DPPH racical scavenging activities in the methanol
extract were attributed to 10(E),12(Z)-CLA (Fig. 1). The biosynthetic pathway of
10(E),12(Z)-CLA in Basidiomycetes-X will be elucidated in the future.
Both ergosterol and CLA are detected in button mushrooms [29], but the additive
or synergistic effects of these compounds are unknown. We demonstrated that
purified CLA was degraded during storage at 4 C for 2–3 months,
probably due to oxidation of CLA, although CLA in the crude fraction before HPLC
purification and CLA in Basidiomycetes-X powder were rather stable. This
suggests the presence of stabilizer(s) for CLA, and such antioxidative
compound(s) in Basidiomycetes-X that need to be verified in future
studies.
DDMP is known as a strong antioxidant [36, 37, 38, 39] that can be formed from hexose in
a nonenzymatic manner [24, 40, 41, 42], and the thermal degradation of D-glucose to
form DDMP has been reported [39, 42, 43]. DDMP inhibits tyrosinase activity,
which is involved in the initial reaction of melanin formation from phenolic
substrates and is thus attractive to cosmetic and medical applications [36]. DNA
strand-breaking activity and mutagenicity of DDMP have been reported [44], and
this can be a harmful function against health. From the point of view of health
promotion, the inhibition of colon cancer cell growth by inducing apoptotic cell
death via the inhibition of NF-B [45], the increase of brown adipose
tissue sympathetic nerve activity and the body temperature above the
interscapular brown adipose tissue [46], and the anti-inflammatory activity by
carrageenin-induced rat hind paw edema method [47] are reported as positive
functions of DDMP.
Three different kinds of bioactive compounds with radical scavenging activity,
ergosterol, 10(E),12(Z)-CLA and DDMP, were identified in the edible mushroom
Basidiomycetes-X. These compounds are the components of the radical
scavengers reported in Basidiomycetes-X extracts [13] and are expected
to be involved in the medicinal effects reported in Basidiomycetes-X [12]. Although they may function additionally or synergistically, further studies
are needed to specify their pharmacological functions.
Uridine is a pyrimidine nucleoside consisting of uracil and ribose that are
linked via a -N1-glycosidic bond. Uridine is thought to have helpful
functions that regulate various biological systems and can be used as a medicine
for the circulatory, respiratory, reproductive, and nervous systems and as an
anticancer treatment and antiviral therapy [48]. Diabetes-induced peripheral
nerve neuropathy [49] and developmental delays associated with increased
nucleotidase activity [50] can be treated with oral uridine. The latest studies
to show that supplementation with uridine and pyruvate protects the proliferative
capacity of T lymphocytes, cell-mediated immunity effector cells, from
mitochondrial toxic antibiotics [51] and that administration of guanosine or
uridine can reduce lung inflammation in OVA-induced asthmatic mice [52].
Adenosine is a purine nucleoside consisting of adenine and ribose that are
linked via a -N9-glycosidic bond. Adenosine is not only used as a part
of various biomolecular components but also functions as a signaling molecule
received by adenosine receptors and has physiological activities. Adenosine
receptors belong to the G-protein coupled receptor family and distribute in human
tissues widely. They are known to participate in physiopathological responses,
which include vasodilation, pain, and inflammation [53]. Therefore, it is
believed that adenosine has a variety of pharmacological effects and can be used
to treat diseases. Adenosine has been used in clinical medicine for emergency
treatment of arrhythmia [54] and is believed to be an anti-inflammatory agent at
the A receptor [55, 56]. Recently, it has been reported that the adenosine
A receptor can inhibit the onset of pulmonary inflammation and thrombosis
caused by COVID-19 [57]. Adenosine has also been shown to be useful in cancer
immunotherapy [58, 59, 60, 61]. Moreover, adenosine receptors are highly expressed in the
brain, and caffeine functions as an adenosine A receptor antagonist, which
suggests that adenosine is an important short-lived autocrine/paracrine mediator
of central nervous system functions [62].
Both pyrimidine and purine nucleosides, uridine and adenosine, respectively,
were detected at similar levels in the Basidiomycetes-X powder (Table 2), although it is unclear whether these complementary bases interact with each
other. We have identified water-soluble compounds that exhibit UV absorption,
namely, DDMP, uridine, adenosine,
4-[2-formyl-5-(hydroxymethyl)-1H-pyrrol-1-yl] butanoic acid, and
4-[2-formyl-5-(hydroxymethyl)-1H-pyrrol-1-yl] butanamide (Fig. 4, Tables 1,2, Ref. [19]). There are relatively large amounts of the components (Table 2),
and their chemical structures have been determined by direct spectroscopic
measurements using purified products (this study, [19]). The
Basidiomycetes-X water extract contains medicinal ingredients that show
anti-obesity effects in mice [15], and the water-soluble compounds identified
thus far (Table 1) may be involved in the pharmacological effects in mice. This
will be verified as a future study. However, there is a possibility that other
compounds without UV absorption may have strong physiological activities. Thus,
we will continue to characterize bioactive compounds in the novel mushroom
Basidiomycetes-X (Echigoshirayukidake) focused on various research
approaches.