September 2005
1777
Coumaric acid (4) was also irradiated in the solid state. (E)-
p-Coumaric acid crystals (1.0 g) were dispersed in hexane in
a Pyrex flask. The flask was then irradiated with a 400 W
high-pressure mercury lamp (Riko, Japan, UVL-400HA) at
room temperature. After 1 d, the product was filtered off,
washed with ether, and recrystallized twice from ethanol to
give 980 mg of white crystals as 4,4ꢀ-dihydroxy-a-truxillic
acid. mpꢂ300 °C (lit. 340 °C). Anal. Calcd for C H O : C,
1
8
16
6
6
5.85%; H, 4.91%. Found: C, 65.75%; H, 4.92%. Positive
ꢃ
1
FAB-MS m/z (rel. int.): 329 [MꢃH] . H-NMR (DMSO-d )
6
d: 3.64 (2H, m, b,bꢀ-H), 4.13 (2H, m, a,aꢀ-H), 6.69 (4H, d,
Jꢄ8.8 Hz, 3,3ꢀ,5,5ꢀ-H), 7.11 (4H, d, Jꢄ8.8 Hz, 2,2ꢀ,6,6ꢀ-
9
)
H).
Fig. 2. Activities of a-Truxillic Acid (1), 4,4ꢀ-Dihydroxy-a-truxillic Acid
Formalin Test and Treatments This method repre- (2), (E)-Cinnamic acid (3), (E)-p-Coumaric Acid (4) and Incarvillateine (5)
sented a modification of that described by Dubuisson and
Dennis. Male ddy mice (25 gꢅ5) were used. The test drugs
40 mg/kg for 1, 2, 3 and 4; 20 mg/kg for 5) were prepared as
against Neurogenic Pain Response (Early Phase) Induced by Formalin in
Mice
10)
Each value represents meanꢅS.E. (nꢄ10). Significant differences (pꢄ0.01) between
control and drug-treated groups are indicated by **.
(
suspensions with 0.5% Tween 80/saline and intraperitoneally
administered 10 min prior to the injection of an inducer (1%
formalin/saline, 20 l). The mice were observed for 30 min
and the time that the mice spent licking the injected right
hindpaw was recorded. The nociceptive scores normally
peaked 0 to 10 min after formalin injection (early phase) and
1
0 to 30 min (late phase) after the injection, representing the
11)
neurogenic and inflammatory pain responses, respectively.
The time spent licking the injected paw was recorded and the
data were expressed as total licking time in the early phase
and late phase.
Statistical Analysis All values are expressed as the
meanꢅS.E. (nꢄ10). For statistical analysis, one-way analysis
of variance combined with Dunnett’s multiple range test for
multiple comparisons were used. Differences were consid-
ered significant at pꢆ0.01.
Fig. 3. Activities of a-Truxillic Acid (1), 4,4ꢀ-Dihydroxy-a-truxillic Acid
(
2), (E)-Cinnamic Acid (3), (E)-p-Coumaric Acid (4) and Incarvillateine (5)
against Inflammatory Pain Response (Late Phase) Induced by Formalin in
Mice
Each value represents meanꢅS.E. (nꢄ10). Significant differences (pꢆ0.01) between
control and drug-treated groups are indicated by **.
RESULTS AND DISCUSSION
The formalin-induced licking response has been used as a
11,12)
model for evaluating new analgesics.
The duration of the pene alkaloidal derivatives derived from Incarvillea sinensis
nociceptive response induced by formalin can be divided into and displayed more potent antinociceptive activity than mor-
two phases. The early phase is from 0 to 10 min after forma- phine in the formalin test. Structure–antinociceptive activity
lin injection and the late phase is from 10 to 30 min after the studies of incarvillateine suggested that the dimeric structure
injection. The two phases have obvious differential proper- played an important role in the expression of its anti-inflam-
ties. The pain in the early phase is evoked by the direct stim- matory activity. a-Truxillic acid has the same dimeric struc-
ulation of the nerve fibers, while and that in the late phase is ture as that of incarvillateine (5). In order to investigate the
due to the inflammatory response. Centrally-acting drugs function of dimeric structure in the anti-inflammatory activi-
such as morphine inhibit both the early and late phases ties of a-truxillic acid and its derivatives, a-truxillic acid (1)
equally. On the other hand, peripheral-acting drugs such as and 4,4ꢀ-dihydroxy-a-truxillic acid (2) as well as their
aspirin inhibit only the late phase.
monomer components (E)-cinnamic acid (3) and (E)-p-
Intraperitoneal administration of 1, 2, 3 and 4 at doses of coumaric acid (4) were prepared and their activities evaluated
0 mg/kg and incarvillateine (5) at a dose of 20 mg/kg, in the formalin test.
4
showed significant antinociceptive activity against both neu-
In the present study, a-truxillic acid (1) and its derivative
rogenic (early phase) and inflammatory (late phase) pain re- 4,4ꢀ-dihydroxy-a-truxillic acid (2) at doses of 40 mg/kg
sponses induced by formalin. a-Truxillic acid (1) and its de- showed weak or no activity against the neurogenic pain re-
rivative 4,4ꢀ-dihydroxy-a-truxillic acid (2) at doses of sponse induced by formalin, while the activity against the in-
4
0 mg/kg showed significant activity against the inflamma- flammatory pain response was equal to that of incarvillateine
tory pain response that was as strong as 5 at a dose of (5) at the dose of 20 mg/kg. Meanwhile their monomer com-
0 mg/kg, while their monomer components (E)-cinnamic ponents (E)-cinnamic acid (3) and (E)-p-coumaric acid (4) at
2
acid (3) and (E)-p-coumaric acid (4) did not show any activ- doses of 40 mg/kg did not show any activity against either
ity against either the neurogenic or inflammatory pain re- the neurogenic or inflammatory pain responses in the forma-
sponses (Figs. 2, 3).
lin test. These results suggested that the dimeric structure
Incarvillateine (5) is representative of the novel monoter- played an important role in the expression of activity against
Chi, Yu-Ming
