Curcumin in fish PDF

Biochemical
Pharmacology,
Copyright 0 1996 Elsevier
Vol. 52, pp. 519-525,
Science Inc.
ISSN
1996.
0006-2952/96/$15.00
+ 0.00
PII SOOOS-2952(96)00302-4
ELSEVIER
Involvement
Antioxidative
of the P-Diketone Moiety in the
Mechanism of Tetrahydrocurcumin
Yasunori Sugiyamu, Shunro Kawakishi and Toshihiko Osawa”
DEPARTMENT OF APPLIED BIOLOGICAL SCIENCES,
NAGOYA UNIVERSITY, NAGOYA 464-01,
ABSTRACT.
major
We examined
metabolites
butylhydroperoxide.
investigate
the inhibitory
of curcumin,
effects
The results demonstrated
the mechanism
of curcumin
on the lipid peroxidation
that THC
of antioxidative
activity,
and tetrahydrocurcumin
of erythrocyte
membrane
showed a greater inhibitory
we examined
the effects
JAPAN
(THC),
ghosts
one of the
induced
by tert-
effect than curcumin.
of several
inhibitors,
To
such as
enzymes, hydroxyl radical scavengers, IO, quencher, and chelating agents for metal ions. Given that
all inhibitors failed to inhibit membrane peroxidation, THC must scavenge radicals such as tert-butoxyl radical
and peroxyl radical. To clarify the antioxidative mechanism of THC, in particular the role of the P-diketone
moiety, dimethylated THC was incubated with peroxyl radicals generated by thermolysis of 2,2’-azobis(2,4antioxidant
dimethylvaleronitrile).
Four
dimethoxybenzoic
acid,
fourth oxidation
product
oxidation
products
seems to be an unstable
mined. These results suggest that the B-diketone
of the C--C
THC
bond at the active
logical properties
KEY
The
rhizome
widely
methylene
is one of the major metabolites
WORDS.
moiety of THC
coloring
between
agent
(turmeric)
has
and spice
three
of which
and its detailed
were
must exhibit
two carbonyls
it may also exhibit
structure
identified
been
antioxidative
activity
by cleavage
moiety.
the same physiological
Because
and pharmaco-
moiety as well as phenolic
B-diketone;
antioxidant;
radical scavenger
Holder et al. [12] did not find any free or conjugated curcumin in the bile after intravenous
administration
of
the treatment of inflammatory and other diseases [l]. Curcumin (diferuloylmethane,
Fig. 1) has been identified as the
[3H]curcumin; according to them, one of the major metabolites in the bile is the glucuronide conjugate of THCt (Fig.
1). THC, a colorless compound less polar than curcumin,
major pigment in turmeric and has been reported to possess
both antioxidative
and antiinflammatory
activities [2-61.
Recent studies indicate that curcumin inhibits the micro-
absorption from the intestines. THC
the physiological and pharmacological
some-mediated
min.
foods,
and it has also been
used in indigenous medicine for
The
1996.
tetrahydrocurcumin;
in many
as 3,4acid.
has not been deter-
in the B-diketone
in viva by means of the B-diketone
PHARMACOL 52;4:519-525,
longa Linn
of Curcuma
used as a yellow
intermediate,
of curcumin,
Curcuma longa Linn; curcumin;
detected,
and 3-(3,4-dimethoxyphenyl)-propionic
carbon
as the active form of curcumin
hydroxy groups. BEHEM
were
3’,4’-dimethoxyacetophenone,
mutagenicity
of benzo[u]pyrene
and 7,12-
seems to be the transformed
product of curcumin
during
may be involved in
properties of curcu-
dimethylbenz[a]anthracene
[7], and that it also acts as a
strong inhibitor of tumor promotion in mouse skin by 12-
In the course of our investigation to find novel types
of antioxidative
substances in plant materials, two B-
O-tetradecanoylphorbol-13-acetate
[8].
Several studies on the absorption and metabolism
diketone-type
antioxidants,
TTAD
and 4-hydroxytritriacontan-16,18-dione,
were isolated and identified as
of cur-
cumin have been reported. Ravindranath
and Chandrasekhara have reported on the absorption and tissue distribution of curcumin in rats [9, lo] and its in viva absorption after oral administration
using [3H]curcumin
[ll].
Their results show that curcumin is transformed during absorption from the intestines and that the transformed product, which is a less polar and colorless compound than
curcumin, enters the serosal side. On the other hand,
*Corresponding
author: Dr. Toshihiko Osawa, Laboratory of Food and
Biodynamics, Department of Applied Biological Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-01, Japan. Tel. 01 l-81-52-7894126; FAX 011-81-52-789-4120.
Received 19 June 1995; accepted 26 February 1996.
novel natural antioxidants from Eucalyptus leaf wax [13,
141. Because curcumin also has a B-diketone moiety, this
moiety must play an important role in the antioxidative
activity of curcumin in uiuo. However, the antioxidative
mechanism
of B-diketone-type
antioxidants
is not clear.
t Abbreuinnons: THC, tetrahydrocurcumin;
TTAD, n-tritriacontan-16,18dione; CLA, conjugated dienoic derivatives of linoleic acid; t-BuOOH,
rert-buoilhydroperoxide;
PtO,, platinum oxide; AMVN, 2,2’-azobis(2,4dimethylvaleronitrile);
AAPH,
2,2’-azobis(2-amidinopropane)dihydrochioride;
DTPA, diethylenetriamine-N,N,N’,N”,N”-pentaacetic
acid; DABCO, 1,4-diazabicyclo-[2,2,2] oc t ane; TBA, 2-thiobarbituric
acid;
SOD, superoxide dismutase; DMTHC, dimethoxytetrahydrocurcumin;
and TBARS, TBA-reacting
substance.
520
Y. Sugiyama et al.
0
0
OCH,
Hydrogenation
Pt02
OH
Curcumin
Tetrahydrocurcumin
FIG. 1. Preparation
Recently,
inhibits
of tetrahydrocurcumin
Hirose et al. [15] reported that TTAD
hepatic
and pancreatic
carcinogenesis.
(THC) from curcumin by hydrogenation
strongly
Moreover,
Pariza and Ha [16] reported that CLA are effective in inhibiting benzo[a]pyrene-induced
forestomach neoplasia in
mice and also in suppressing the process of tumor promotion in the mouse forestomach [16]. One of the possible
(THC)
with PtO,.
Uehara et nl. [18]. After hydrogenation, THC was purified
by preparative TLC (5% MeOH in CHCl,, R, = 0.86) with
a yield of 42.5%.
The
identity
and purity of THC
were
confirmed by using MS, IR, UV, and NMR spectra. THC:
FAB-MS m/s 395 (M + Na)‘; IR (KBr) v,,, 3430 (OH),
3060-2840
(CH),
1603 (C=O),
1033 (OCH,,)cm-‘;
mechanisms for the anticarcinogenicity
of CLA is thought
to be that an oxidized derivative of CLA must be the actual
ultimate antioxidant form rather than CLA itself, although
UV(EtOH)
Xm,,(log E) 225(4.16), 282(4.24) nm; ‘H NMR
(CDCl,) 6 2.54 (4H, t,J = 8.1 Hz, 1, 7), 2.74-2.88 (4H, m,
the structure of the active form has not been determined.
(lH(enol),
s, 4), 5.65 (2H, broad, OH), 6.65 (2H, d,J = 7.8
Hz, 6’, 6”), 6.67 (2H, s, 2’,2”), 6.81 (2H, d, J = 7.8 Hz,
5’,5”).
However, it has been suggested that the introduction
P-diketone
moiety
into the CLA
molecule
of the
is the most
likely candidate as the active form of CLA [ 171. Therefore,
it is very important to investigate the antioxidative mechanism of B-diketone-type
antioxidants.
In this study, we examined
the inhibitory
effects of cur-
cumin and THC on t-BuOOH-induced
lipid peroxidation.
To investigate the mechanism of antioxidative activity, we
examined
the contribution
of oxidizing species in the per-
oxidation system. This paper also gives details on the antioxidative mechanism at the B-diketone moiety of THC
and reports on an investigation of the metabolic
THC in reaction with peroxyl radicals.
MATERIALS
pathway of
was obtained
after purification
by preparative
silica gel TLC (5% MeOH in CHCl,, Merck Art. 13895)
from turmeric, which was a gift from the Daiwa Kasei Co.,
Ltd., Saitama, Japan. The yield of curcumin was 76.0%.
PtOz,
AMVN,
AAPH,
mannitol,
DABCO, 3,4_dimethoxybenzaldehyde,
DMSO,
DTPA,
and acetyl acetone
were purchased from Wako Pure Chemical
Industries Ltd.,
Osaka, Japan. TBA was purchased from Merck (Darmstadt,
F.R.G.). Egg yolk phosphatidylcholine,
SOD (from bovine
erythrocytes),
and catalase (from bovine liver) were purchased from the Sigma Chemical Co. (St. Louis, MO,
U.S.A.). Commercially available rabbit blood was obtained
from Japan Biotest Laboratories Inc. (Kokubunji, Tokyo,
Japan). t-BuOOH was purchased from the Tokyo Kasei Kogyo Co., Ltd., Tokyo, Japan.
Preparation
of Curcuminoid
THC. Curcumin
tion with PtO,
s, 4), 3.83
to THC
as the catalyst according
(6H,
s, OCH,),
5.42
DMTHC. DMTHC was prepared synthetically by condensation of 3,4-dimethoxybenzaldehyde
and acetyl acetone by
the method
of Pabon
[19]. The
identity
of the synthetic
compound was established by using MS, IR, UV, and NMR
spectra. Dimethoxycurcumin
was reduced to DMTHC by
hydrogenation with PtO, as described above. DMTHC was
purified by preparative TLC (n-hexane:ethyl
acetate = 1: 1,
R, = 0.53) with a yield of 52.0%. The identity and purity
were confirmed
by using MS, IR, UV, and NMR spectra.
DMTHC: EI-MS m/z 400 (M’); IR (KBr) v,,, 2937 (CH),
1592 (C=O), 1029 (OCH,) cm’; UV (EtOH) &_(log
E)
228(4.23), 280(4.26) nm; ‘H NMR (CDCl,) 6 2.57 (4H, t,
(4H, m, 2,6), 3.53 (2H(keto),
4), 3.866-3.871
(12H, m, OCH,),
6.72-6.82
(6H, m, 2’,5’,6’,2”,5”,6”).
5.46
(lH(enol),
s,
s, 4),
Antioxidatiwe Assay
Commercially
available rabbit blood (100 mL) was diluted
with 300 mL of isotonic buffer solution (10 mM phosphate
buffer, pH 7.4/152 mM NaCl). After centrifugation (1500
g, 20 mm), the blood was lysed in 300 mL of 10 mM
phosphate buffer, pH 7.4. Erythrocyte membrane ghosts
were pelleted by centrifugation (20,000 g, 40 min), and the
precipitate was diluted to give a suspension (1 .O mg protein/
mL). Peroxidation of the erythrocyte membrane ghosts induced by t-BuOOH was carried out by a method described
previously [20]. After incubation at 37” for 20 min, the
formation of TBARS was determined at 532 nm.
Preparation of Liposotnes
Derivatives
was converted
(2H(keto),
_I = 7.8 Hz, 1,7), 2.82-2.91
AND METHODS
Materials
Curcumin
2, 6), 3.49
by hydrogena-
to the method of
Liposomes were prepared from egg yolk phosphatidylcholine. Egg yolk phosphatidylcholine
was suspended in 10
Antioxidative Mechanism of Tetrahydrocurcumin
521
mM phosphate buffer (pH 7.4) and vortexed. Liposomes
were always handled in an atmosphere of nitrogen, to prevent auto-oxidation.
OGdation
of DMTHC
DMTHC ( 100 kmol) and AMVN (3 mmol) were dissolved
in oxygen-saturated acetonitrile and incubated in a screwcap test tube at 37” according to the method of Liebler et al.
[21]. AMVN was used in order to replicate the method of
Liebler et al. [21] on a larger scale. DMTHC (4 kmol) incorporated in the liposomes (10 mg/mL phosphate buffer)
and AAPH (200 p_mol) were incubated in a screw-cap test
tube at 37”. AAPH was used instead of AMVN in the
liposome experiment because AMVN is insoluble in phosphate buffer. Oxidation
OJ
0
products were analyzed by reverse-
50
phase HPLC on a Develosil ODS-5 column (4.6 x 150 mm)
(Nomura Chemical Co., Ltd.). An aliquot of the reaction
mixture was eluted with a linear gradient of a two-solvent
system at a flow rate of 1.0 mL/min. Solvent
trifluoroacetic
acid:methanol
82) and solvent
A (0.1%
B (100%
methanol) were used for the gradient. The gradient employed was as follows: 100 to 0% A in 30 min, isocratic at
0% A for 10 min, 0 to 100% A in 10 min. The elution was
monitored by absorbance at 280 nm. The peak area was
determined by use of a Shimadzu C-R3A Chromatopac.
200
150
250
Concentration (PM)
FIG. 2. Inhibitory effects of curcumin and THC on the Lipid
peroxidation of erythrocyte membrane ghosts induced by
t-BuOOH.
After erythrocyte membrane ghosts at a concentration of 1.0 mg protein/ml were incubated with 2.0 mM
t-BuOOH
for 20 min in the presence or absence of each
curcuminoid, TBARS formation was determined at 532 nm.
A control containing no added curcuminoids represented
100% lipid peroxidation (1.66 pM MDA equivalents). Results are the means * SD from four separate experiments.
information
RESULTS
100
on the role of the B-diketone
moiety of THC,
the antioxidative effect of the phenolic hydroxyl groups was
blocked by methylation of the groups. The dimethylated
THC was prepared by hydrogenation
of curcumin with
PtO, as the catalyst (Fig. 1). All olefinic protons in the ‘H
THC,
NMR spectra of curcumin were found to disappear in the
‘H NMR spectrum of THC. All spectroscopic data of THC
thetic compound with PtO,, after dimethoxycurcumin
was
prepared as shown in Materials and Methods. The identity
were identical with those described in a previous paper on
this compound [22].
We examined the inhibitory effects of curcumin and
and purity of the synthesized DMTHC
THC,
AMVN at 37” in oxygen-saturated acetonitrile.
dependent reaction of DMTHC with AMVN
which is one of the major metabolites
of curcumin,
on the lipid peroxidation of erythrocyte membrane ghosts
induced by t-BuOOH.
Concentration-dependent
inhibition was observed, and THC exhibited a greater inhibitory
effect than curcumin, especially at 150 p,M (Fig. 2). To
investigate the mechanism of antioxidative activity, we examined what kind of oxidizing species are involved in the
lipid peroxidation. We investigated the effects of inhibitors
of active oxygen species, such as antioxidant enzymes, hydroxyl radical scavengers (mannitol
and DMSO),
‘0,
quencher (DABCO),
and chelating agents for metal ions
(DTPA),
on the lipid peroxidation of erythrocyte membrane ghosts by determining TBARS formation. As shown
in Fig. 3, all inhibitors failed to inhibit membrane peroxidation. This result supported the previously reported result
that tert-butoxyl radical may be the oxidizing species in
lipid peroxidation [23]. THC must scavenge radicals, such
as alkoxyl radical or peroxyl radical, and these effects are
superior to curcumin.
The antioxidative mechanism of THC, especially at the
@-diketone
moiety, was also investigated.
To obtain more
DMTHC,
was obtained by hydrogenation
of the syn
were confirmed
by
using MS, IR, UV, and NMR spectra. DMTHC was incubated with peroxyl radicals, generated by the thermolysis of
The timewas exam-
ined by reverse-phase HPLC on a Develosil ODS-5 column.
Four oxidation products were detected as shown in Fig. 4A.
Peaks 1, 2, and 3 were found to increase with incubation
time. On the other hand, peak 4 decreased gradually after
33 hr of incubation (Fig. 5). This result suggests that peak
4 must be an unstable
intermediate
in the reaction
of
DMTHC with AMVN. The reaction mixture was rapidly
chilled by immersion in ice at 33 hr, and the reaction was
stopped to determine the structure of peak 4. These four
products were isolated and characterized. The proposed
structures of the isolated peaks l-3 are shown in Table 1;
identification was performed by ‘H NMR and EI-MS. Isolated peak 4 was also investigated. The ‘H NMR spectrum
of the product suggested the possibility of the presence of
hydroperoxide,
although the detailed structure has not
been determined. We also used the liposome model in order
to mimic the erythrocyte membranes. DMTHC incorporated in the liposomes was incubated with AAPH, which
generates peroxyl radicals similarly to AMVN. As a result
522
Y. Sugiyama et al.
lase, mannitol, DMSO, DABCO, and DTPA) failed to inhibit membrane peroxidation, tert-butoxyl radical may be
the oxidizing species in lipid peroxidation as reported previously [23], and THC must scavenge radicals such as alkoxyl radical and peroxyl radical. Even though the concentration used was high (10 mM), the approximately 40%
inhibition of lipid peroxidation by DABCO suggests that
either singlet oxygen has a minor role in the t-BuOOHinduced lipid peroxidation
process or, more likely, DABCO
is also a poor scavenger of alkoxyl or peroxyl radicals.
We have found two novel B-diketone-type antioxidants,
TTAD and 4-hydroxy-tritriacontan-16,18-dione
[13, 141.
Recently, Hirose et al. [15] reported that TTAD
inhibits hepatic and pancreatic carcinogenesis.
simple
B-diketones
strongly
Several
such as 1,l ,l-trifluoroacetylacetone,
DMTHC
4
FIG. 3. Effects of inhibitors on the lipid peroxidation of
erythrocyte membrane ghosts induced by t-BuOOH.
After
erythrocyte membrane ghosts at a concentration of 1.0 mg
protein/mL were incubated with 2.0 mM t-BuOOH
for 20
min in the presence or absence of various active oxygen
scavengers, the formation of TBARS was determined at 532
nm. A control containing no added scavengers represented
100% lipid peroxidation (2.26 PM MDA equivalents). Res
suits are the means * SD from four separate experiments.
L/
of the reaction, three oxidation products (peaks l-3) have
been identified based on similar retention times as the
peaks l-3
detected
obtained with AMVN;
(Fig. 4B). DMTHC
ucts in both oxidation
DMTHC
however, peak 4 was not
gave the same reaction
1,
prod-
model systems.
DISCUSSION
Given
that THC
must be the transformed
product of cur-
cumin during absorption from the intestines [9-121, the
transformed THC must be transported in blood and distributed in some tissues such as liver or kidney. We examined
the inhibitory effects of curcumin and THC on the lipid
peroxidation of erythrocyte membrane ghosts induced by
t-BuOOH. The result demonstrated that THC showed a
greater inhibitory effect that curcumin, especially at 150
p,M (Fig. 2). Curcumin has been reported to act as a strong
inhibitor of mutagenicity
[7] and tumor promotion
in
mouse skin by 120-tetradecanoylphorbol-13-acetate
[8].
Therefore, THC may have more effective antimutagenicity
or antitumor activity than curcumin.
We examined oxidizing species in the lipid peroxidation
of erythrocyte membrane ghosts to investigate the mechanism of antioxidative activity. We investigated the effects
of several inhibitors on lipid peroxidation by determining
TBARS formation. Because all inhibitors used (SOD, cata-
10
Retention Time (min)
FIG. 4. HPLC profile of DMTHC
oxidized with AMVN
(A)
and AAPH (B). DMTHC
(100 pmol) was incubated with 3
mmol AMVN
for 33 hr (A), and DMTHC
(4 pmol) incor#
porated into the liposomes (10 mg/mL phosphate buffer)
was incubated with 200 pmol AAPH
for 94 hr (B). An
aliquot of the solution was submitted for reverse-phase
HPLC on a Develosil ODS-5 column (4.6 x 150 mm) as
described in Materials and Methods.
Antioxidative
523
Mechanism of Tetrahydrocurcumin
dative effect of the phenolic
blocked by methylation
the p-diketone
hydroxy groups of THC
moiety alone on the antioxidative
nism was investigated.
Dimethylated
prepared as described in Materials
exhibited
was
of the groups, and then the role of
approximately
THC,
and Methods.
36% inhibition
mecha-
DMTHC,
(64.15
was
DMTHC
& 0.006%
lipid peroxidation) at 150 FM on the lipid peroxidation
erythrocyte membrane ghosts induced by t-BuOOH.
Peroxyl radicals are known to be the chain-carrying
cals in lipid peroxidation,
and their reactions
erol, one of the phenolic-type
antioxidants,
-0
20
40
60
100
80
Reaction Time (hr)
FIG. 5. Time-dependent
changes of oxidation products of
DMTHC during incubation with AMVN.
DMTHC
at a concentration of 100 pmol was incubated with 3 mmol AMVN.
An aliquot of the solution was submitted for reverse-phase
HPLC on a Develosil ODS-5 column (4.6 x 150 mm), and
the peak area was determined by use of a Shimadzu C-R3A
Chromatopac as described in Materials and Methods.
peroxyl
radicals
carboxyl)-propane]
generated
reactions with peroxyl
Given this background,
oxyl
radicals,
AMVN
which
were generated
mechanism
by thermolysis
acetonitrile,
found to increase with incubation
time and were identified
detailed structure
e
suggesting that it must be an unstable intermediate
reaction
of DMTHC
acid
the
of isolated peak 4 has yet to be deter-
‘H NMR
EI-MS
8 (ppm)
(m/z)
3.95
3.96
6.92
7.59
7.77
(3H,
(3H,
(lH,
(lH,
(IH,
s)
s)
d, _I = 8.4)
d, J = 1.9)
dd, I = 8.4, 1.9)
182 (M’)
167
2.58
3.95
3.94
6.90
7.53
7.59
(3H,
(3H,
(3H,
(lH,
(lH,
(lH,
s)
s)
s)
d, J = 8.3)
d, J = 2.0)
dd, I = 8.3, 2.0)
180 (M’)
165
137
77
t, ] = 7.7)
t, I = 7.7)
s)
s)
(3H, m)
210 (M’)
151
121
91
77
0
3-(3,4-Dimethoxyphenylj-propionic
in the
with peroxyl radicals. Although
mined, the ‘H NMR spectrum suggests the possibility of the
presence of hydroperoxide. From these data, an antioxidative mechanism of DMTHC (P-diketone moiety of THC)
is proposed, as shown in Fig. 6. Both enol and keto forms of
product
C
acid, respec-
tively. Peak 4 decreased gradually after 33 hr of incubation,
TABLE 1. Structures and analytical data for oxidation products of DMTHC
H&O
antioxi-
acid, 3’,4’-dimethoxyacetophe-
of P-diketone-type
antioxidants. Because THC, one of the
major metabolites of curcumin, also has a p-diketone moiety, which may play an important role in antioxidative
OH
of
to confirm
of P-diketone-type
none, and 3-(3,4-dimethoxyphenyl)-propionic
H&O
the
dants. Four oxidation products were detected by reversephase HPLC as shown in Fig. 4A. Peaks 1, 2, and 3 were
acetylacetone, benzoylacetone and dibenzoylmethane
were
reported to inhibit mutagenicity induced by 2-nitrofluorene
using the Salmonella typhimurium strain [24]. Therefore, it is
very important to investigate the antioxidative mechanism
Oxidation
Yamauchi
radicals generated from AMVN.
DMTHC was incubated with per-
as 3,4-dimethoxybenzoic
activity, we examined the antioxidative mechanism of the
P-diketone-type
antioxidants by using THC. The antioxi-
azobis[(n-butyl-
[27] also have reported
at 37” in oxygen-saturated
the antioxidative
For example,
of tocopherol
and azobis(isobutyronitrile).
[26] and Matsuo et al.
et al.
from
radi-
with tocoph-
have been stud-
ied by numerous investigators [21, 25-271.
Winterle et al. [25] reported the reactions
with
of
2.67 (2H,
2.92 (2H,
3.86 (3H,
3.87 (3H,
6.74-6.82
524
Y. Sugiyama et al.
0
0
H&O
OCH,
H&O
OCH,
ROO .
HQ
\
0
0
0
H&O
OCH,
H&O
OCY
H&O
OCY
H&O
OCH3
;;IdOH
,““;-
;z&f+J;;;
3
3
3
H
3-(3,4-Dimethoxyphenyl)-propionic
02
acid
ROO1
b
1
co2
L
0
(ROO
l
co2
0
: Peroxyl radicals)
H&O
H,CO
3’,4’-Dimethoxyacetophenone
FIG. 6. Proposed antioxidative mechanism
DMTHC must scavenge free radicals, and the C-C
bond
at the active methylene carbon between two carbonyls in
the p-diketone
moiety is cleaved. As a result, 3-(3,4dimethoxyphenyl)-propionic
acid was formed, and 3,4dimethoxybenzoic
acid and 3’,4’-dimethoxyacetophenone
were produced as secondary oxidation
products. This
mechanism has been confirmed by the reaction of DMTHC
incorporated in the liposomes with AAPH, because the
3,4-Dimethoxybenzoic
acid
of DMTHC.
same three oxidation products have been identified (Fig.
4B). These results strongly support the conclusion that the
P-diketone moiety must play an important role in the antioxidative mechanism of THC. Although many workers
[21, 25-271 have reported on phenolic-type natural antioxidants including tocopherol, this is the first report to
show the involvement of the P-diketone moiety in antioxidative mechanisms.
Antioxidative
This
Mechanism
study on the antioxidative
ketone-type
antioxidants
indicates
moiety may play an important
antimutagenesis
type antioxidants
inhibit
addition,
of curcumin
expected
such as TTAD
because THC
the
of P-diP-diketone
of
13.
because P-diketonehave been reported
and carcinogenesis
to
[7, 8, 151. In
is the rapidly metabolized
during absorption
that THC
mechanism
that
role in the elucidation
or anticarcinogenesis,
tumor promotion
525
of Tetrahydrocurcumin
product
from the intestines,
may have the same important
15.
it is
physi-
ological and pharmacological properties as the active form
of curcumin in vioo by means of the P-diketone moiety as
well as phenolic hydroxy groups. A detailed
testing this conclusion is underway.
14.
16.
experiment
17.
References
1. Nadkarni
Nadkarni
KM, Curcuma longa. In: Indian Mat&a Medica (Ed.
KM), pp. 414-417. Popular Prakashan, Bombay,
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