Inducible nitric oxide synthase and cyclooxygenase-2 participate in anti-inflammatory activity of imperatorin from Glehnia littoralis

Inducible Nitric Oxide Synthase and Cyclooxygenase-2 Participate in

Anti-inflammatory Activity of Imperatorin from

Glehnia littoralis

Guan-Jhong Huang,

Jeng-Shyan Deng,

Jung-Chun Liao,

Wen-Chi Hou,

Sheng-Yang Wang,

Ping-Jyun Sung,

and Yueh-Hsiung Kuo*

†

_{School of Chinese Pharmaceutical Sciences and Chinese Medicine Resources, College of Pharmacy, China Medical University,}

Taichung, Taiwan

‡

_{Department of Health and Nutrition Biotechnology, Asia University, Taichung 413, Taiwan}

_{School of Pharmacy, College of Pharmacy, China Medical University, Taichung 404, Taiwan}

_{Graduate Institute of Pharmacognosy, Taipei Medical University, Taipei 250, Taiwan}

_{Department of Forestry, National Chung-Hsing University, Taichung 402, Taiwan}

_{National Museum of Marine Biology and Aquarium, Pingtung 944, Taiwan}

∇

_{Graduate Institute of Marine Biotechnology, National Dong Hwa University, Pingtung 944, Taiwan}

_{Agricultural Biotechnology Research Center, Academic Sinica, Taipei, Taiwan, Republic of China}

◆

_{Tsuzuki Institute for Traditional Medicine, China Medical University, Taichung, Taiwan, Republic of China}

ABSTRACT:

In this study, we have investigated the anti-inflammatory effects of imperatorin, a compound isolated from the

roots of Glehnia littoralis, using a lipopolysaccharide (LPS)-stimulated mouse macrophage (RAW264.7) in vitro and a

carrageenan (Carr)-induced mouse paw edema model in vivo. When RAW264.7 macrophages were treated with imperatorin

together with LPS, a significant concentration-dependent inhibition of NO production was detected. Western blotting revealed

that imperatorin blocked the protein expression of iNOS and cyclooxygenase-2 (COX-2) in LPS-stimulated RAW264.7

macrophages significantly. In the anti-inflammatory test, imperatorin decreased the paw edema at 4 and 5 h after Carr

administration and increased the activities of catalase, superoxide dismutase, and glutathione peroxidase in paw edema. We also

demonstrated that imperatorin significantly attenuated the malondialdehyde level in the edema paw at the fifth hour after Carr

injection. Imperatorin decreased the NO and tumor necrosis factor and prostaglandin E2 levels on serum at 5 h after Carr

injection. Western blotting revealed that imperatorin decreased Carr-induced iNOS and COX-2 expressions at 5 h in edema paw.

An intraperitoneal injection treatment with imperatorin also diminished neutrophil infiltration into sites of inflammation as did

indomethacin. The results suggested that imperatorin had anti-inflammatory effects in LPS-stimulated RAW 264.7 cells and

Carr-injected mice, respectively. In addition, inhibition of elevated iNOS and COX-2 protein expression as well as neutrophil

infiltration of Carr-injected paws may be involved in the beneficial effects of imperatorin.

KEYWORDS:

Chinese herb, imperatorin, anti-inflammation, NO, TNF-

α

■

INTRODUCTION

The dried roots and rhizomes of Glehnia littoralis

(Umbelli-ferae) have been used in traditional oriental medicine as

diaphoretic, antipyretic, and analgesic agents in the Taiwan.

Many researcher studies reported that G. littoralis has

anti-oxidant, antitumor, antiamnesic, blood circulation-promoting,

immunomodulatory, and antimicrobial activities.

Quercetin,

isoquercetin, rutin, chlorogenic acid, and caffeic acid have

been isolated as the major antioxidative constituents in the

underground parts of G. littoralis.

Imperatorin is the main

coumarin in the root of G. littoralis. Imperatorin is one of

the furanocoumarins. Furanocoumarins have biological

func-tions including antidiabetic, anticonvulsant, and vascular

vasodilation functions, increased cell differentiation in

osteo-blasts, and reduction in liver steatosis.

Imperatorin has many

medical effects such as anticonvulsant, inflammatory,

anti-tumor, antibacterial, and anticoagulant activities.

However,

little information is available on the anti-inflammatory effects of

imperatorin.

Many studies on plant-derived anti-inflammatory compounds

have investigated the potential inhibitory effects of natural

products in an in vitro system, lipopolysaccharide (LPS)-stimulated

macrophage. Using this system, bacterial LPS has become one of

the best-characterized stimuli used to induce the up-regulation

of proinflammatory proteins such as cyclooxygenase-2 (COX-2)

and inducible nitric oxide synthase (iNOS). Inducible COX-2

could be responsible for the high prostaglandins observed in

much inflammatory pathology.

Papers also have reported that

an inflammatory effect induced by carrageenan (Carr) could be

associated with free radical formation.

Free radical,

prosta-glandin, and nitric oxide (NO) will be released when

administer-ing with Carr for 1−5 h. The edema effect was raised to the

maximum at 3 h, and its malondialdehyde (MDA) production was

Revised: December 19, 2011

Accepted: December 20, 2011

Published: December 20, 2011

due to free radical attack plasma membrane.

Thus, the

inflam-matory effect would result in the accumulation of MDA.

Therefore, in this paper, we examined the anti-inflammatory

effects of imperatorin on LPS-induced RAW264.7 cells and

Carr-induced paw edema in mice, and we detected the levels of

iNOS and COX-2 in either RAW264.7 cell or paw edema. Also,

the activities of catalase (CAT), superoxide dismutase (SOD),

and glutathione peroxidase (GPx) in the paw edema at 5 h after

Carr injection were investigated to understand the relationship

between the anti-inflammatory mechanism of the imperatorin

and the antioxidant enzymes.

■

MATERIALS AND METHODS

Chemicals. LPS (endotoxin from Escherichia coli, serotype 0127:B8), Carr (type IV), indomethacin, MTT (3-[4,5-dimethylth-iazol-2-yl]-2,5-diphenyltetrazolium bromide), and other chemicals were purchased from Sigma Chemical Co. (St. Louis, MO). Tumor necrosis factor (TNF-α) and prostaglandin E2 (PGE2) were purchased from Biosource International Inc. (Camarillo, CA). Anti-iNOS, anti-COX-2, and anti-β-actin antibody (Santa Cruz, United States) and a protein assay kit (Bio-Rad Laboratories Ltd., Watford, Herts, United Kingdom) were obtained as indicated. Poly-(vinylidene fluoride) membrane (Immobilon-P) was obtained from Millipore Corp. (Bedford, MA).

Plant Material. The root of G. littoralis was collected in Tai Chung, Taiwan. The plant material was identified by Muh-Tsuen Gun, formerly a technician of the Department of Botany, National Taiwan University. A voucher specimen has been deposited at the Herbarium of the Department of Botany, National Taiwan University, Taipei, Taiwan.

Isolation and Determination of the Active Compound. Air-dried pieces of G. littoralis root (12 kg) were extracted three times with acetone (12 L) at room temperature (7 days each time). The acetone extract was evaporated in vacuo to leave a black residue, which was suspended in H2O and then partitioned (three times) with 11 L of ethyl acetate (EtOAc). The EtOAc fraction (360 g) was chromato-graphed on silica gel using n-hexane and EtOAc of increasing polarity as an eluent and further purified by high-performance liquid chromato-graphy eluting with n-hexane:EtOAc (25:75). Imperatorin (Figure 1A) was eluted with 10% EtOAc in hexane and recrystallized with EtOH.9 Imperatorin: C16H1404, mp 97.5−99 °C. [M] + m/z 270.0897.1H NMR (CDCl3, 500 MHz): 1.69, 1.71 (each 3H, s), 4.98 (2H, d, J = 7.2 Hz), 5.59 (1H, t, J = 7.2 Hz), 6.33 (1H, d, J = 9.5 Hz, H-3), 6.79 (1H, d, J = 2.1 Hz, H-3′), 7.33 (1H, s, H-5), 7.67 (1H, d, J = 2.1 Hz, H-2′), 7.73 (1H, d, J = 9.5 Hz, H-4).13_{C NMR (CDC1} 3, 125 MHz): 18.0 (q), 25.7 (q), 70.1 (t), 106.6 (d), 113.1 (d), 114.6 (d), 116.4 (s), 119.7 (d), 125.8 (s), 131.6 (s), 139.6 (s), 143.8 (s), 144.3 (d), 146.6 (d), 148.6 (s), 160.6 (s). UVλmax(ε) nm: 218 (22800), 249 (20600), 301 (10600). IR (KBr) cm−1: 1722, 1708 1589, 1150, 838.

Animals. Imprinting control region (ICR; 6−8 weeks, male) mice were obtained from the BioLASCO Taiwan Co., Ltd. The animals were kept in plexiglass cages at a constant temperature of 22± 1 °C and relative humidity of 55± 5% with 12 h dark−light cycle for at least 2 weeks before the experiment. They were given food and water ad libitum. All experimental procedures were performed according to the National Institutes of Health (NIH) Guide for the Care and Use of Laboratory Animals. In addition, all tests were conducted under the guidelines of the International Association for the Study of Pain.10

After a 2 week adaptation period, male ICR mice (18−25 g) were randomly assigned to four groups (n = 6) of the animals in the study. The control group received normal saline (intraperitoneal; ip). The other three groups include a Carr-treated, a positive control (Carr + Indo), and imperatorin-administered groups (Carr + imperatorin).

Cell Culture. A murine macrophage cell line RAW264.7 (BCRC no. 60001) was purchased from the Bioresources Collection and Research Center (BCRC) of the Food Industry Research and Development Institute (Hsinchu, Taiwan). Cells were cultured in plastic dishes containing Dulbecco's modified Eagle's medium (DMEM, Sigma)

supplemented with 10% fetal bovine serum (FBS, Sigma) in a CO2 incubator (5% CO2in air) at 37°C and subcultured every 3 days at a dilution of 1:5 using 0.05% trypsin−0.02% EDTA in Ca2+_{-, Mg}2+_-free phosphate-buffered saline (DPBS).

Cell Viability. Cells (2 × 105_{) were cultured in a 96-well plate} containing DMEM supplemented with 10% FBS for 1 day to become nearly confluent. Then, cells were cultured with imperatorin in the presence of 100 ng/mL LPS for 24 h. After that, the cells were washed twice with DPBS and incubated with 100μL of 0.5 mg/mL MTT for 2 h at 37°C testing for cell viability. The medium was then discarded, and 100μL of dimethyl sulfoxide (DMSO) was added. After 30 min of incubation, the absorbance at 570 nm was read using a microplate reader (Molecular Devices, Sunnyvale, CA).

Measurement of NO/Nitrite. NO production was indirectly assessed by measuring the nitrite levels in the cultured media, and serum was determined by a colorimetric method based on the Griess reaction.11 The cells were incubated with imperatorin (0, 1, 5, and 10μg/mL) in the presence of LPS (100 ng/mL) at 37 °C for 24 h. Then, cells were dispensed into 96-well plates, and 100μL of each supernatant was mixed with the same volume of Griess reagent (1% sulfanilamide, 0.1% naphthyl ethylenediamine dihydrochloride, and 5% phosphoric acid) and incubated at room temperature for 10 min, and the absorbance was measured at 540 nm with a Micro-Reader (Molecular Devices). Serum samples were diluted four times with distilled water and deproteinized by adding 1/20 volume of zinc sulfate (300 g/L) to a final concentration of 15 g/L. After centrifugation at 10000g for 5 min at room temperature, 100μL of supernatant was applied to a microtiter plate well, followed by 100 μL of Griess reagent. After 10 min of color development at room temperature, the absorbance was measured at 540 nm with a Micro-Reader. By using sodium nitrite to generate a standard curve, the concentration of nitrite was measured for absorbance at 540 nm.

Carr-Induced Edema. The Carr-induced hind paw edema model was used for determination of anti-inflammatory activity.12 Animals were ip treated with imperatorin (1, 5, and 10 mg/kg) (dissolved in 0.5% carboxymethylcellulose), Indo (10 mg/kg), or normal saline, 30 min prior to injection of 1% Carr (50μL) in the plantar side of right hind paws of the mice. The paw volume was measured after Carr injection and at 1, 2, 3, 4, and 5 h intervals after the administration of the edematogenic agent using a plethysmometer (model 7159, Ugo Basile, Varese, Italy). The degree of swelling induced was evaluated by the ratio a/b, where a was the volume of the right hind paw after Carr treatment, and b was the volume of the right hind paw before Carr treatment. Indo was used as a positive control. After 5 h, the animals were sacrificed, and the Carr-induced edema feet were dissected and stored at−80 °C. Also, blood was withdrawn and kept at −80 °C.

The right hind paw tissue was taken at 5 h. The right hind paw tissue was rinsed in ice-cold normal saline and immediately placed in cold normal saline four times their volume and homogenized at 4°C. Then, the homogenate was centrifuged at 12000g for 5 min. The supernatant was obtained and stored at−20 °C for MDA assays. The paw tissue was rinsed in ice-cold normal saline and immediately placed in cold normal saline one time their volume and homogenized at 4°C. Then, the homogenate was centrifuged at 12000g for 5 min. The supernatant was obtained and stored at −20 °C for the antioxidant enzyme (CAT, SOD, and GPx) activity assays. The protein concen-tration of the sample was determined by the Bradford dye-binding assay (Bio-Rad, Hercules, CA).

MDA Assay. MDA from Carr-induced edema foot was evaluated by the thiobarbituric acid reacting substances (TBARS) method.13 Briefly, MDA was reacted with thiobarbituric acid in the acidic medium at a high temperature and formed a red complex TBARS. The absorbance of TBARS was determined at 532 nm.

Measurement of TNF-α and PGE2 by an Enzyme-Linked Immunosorbent Assay (ELISA). The levels of TNF-α and PGE2 were determined using a commercially available ELISA kit (Biosource International Inc.) according to the manufacturer's instruction. TNF-α and PGE2were determined from a standard curve.

Determination of Antioxidant Enzyme Activity in Paw Tissue. The following biochemical parameters were analyzed to check

the protective activity of imperatorin in the paw tissues by the methods given below. The total SOD activity was determined by the inhibition of

cytochrome c reduction.14The reduction of cytochrome c was mediated by superoxide anions generated by the xanthine/xanthine oxidase system Figure 1.Chemical structure of imperatorin (A) and the effects of imperatorin on LPS-induced cell viability (B), NO production (C), TNF-α (D), and PGE2(E) in LPS-stimulated RAW264.7 cells. Cells were incubated for 24 h with 100 ng/mL of LPS in the absence or presence of imperatorin (0, 1, 5, and 10μg/mL). Imperatorin was added 1 h before incubation with LPS. The cell viability assay was performed using MTT assay. The nitrite concentration in the medium was determined using Griess reagent. TNF-α and PGE2concentrations in the medium were determined using an ELISA kit. The data were presented as means± SDs for three different experiments performed in triplicate.###p < 0.001 control group as compared to LPS-treated group.*p < 0.05, **p < 0.01, and ***p < 0.001 were compared with the LPS-alone group.

and monitored at 550 nm. One unit of SOD was defined as the amount of enzyme required to inhibit the rate of cytochrome c reduction by 50%. The total CAT activity was based on that of Aebi.15In brief, the reduction of 10 mM H2O2in 20 mM phosphate buffer (pH 7) was monitored by measuring the absorbance at 240 nm. The activity was calculated using a molar absorption coefficient, and the enzyme activities were defined as nanomoles of dissipating hydrogen peroxide per milligram protein per minute. Total GPx activity in cytosol was determined according to Paglia and Valentine's method.16The enzyme solution was added to a mixture containing hydrogen peroxide and glutathione in 0.1 mM Tris buffer (pH 7.2), and the absorbance at 340 nm was measured. The activity was calculated by using a calibration curve of GPx established from bovine whole blood. A linear relationship between the activity (unit/mL) of GPx and the reduction of NADPH absorbance at 340 nm was found, and the enzyme activities were defined as nanomoles of NADPH oxidized per milligram protein per minute.

Protein Lysate Preparation and Western Blot Analysis of iNOS and COX-2. The stimulated murine macrophage cell line RAW264.7 cells were washed with PBS and lysed in an ice-cold lysis buffer [10% glycerol, 1% Triton X-100, 1 mM Na3VO4, 1 mM EGTA, 10 mM NaF, 1 mM Na4P2O7, 20 mM Tris buffer (pH 7.9), 100 mM β-glycerophosphate, 137 mM NaCl, 5 mM EDTA, and one protease inhibitor cocktail tablet (Roche, Indianapolis, IN)] on ice for 1 h, followed by centrifugation at 12000g for 30 min at 4°C. Soft tissues were removed from individual mice paws and homogenized in a solution containing 10 mM CHAPS [3-(3-cholamidopropyl)dimethyl-ammonio]-1- propanesulfonate), 1 mM phenylmethylsulfonyl fluoride (PMSF), 5μg/mL, aprotinin, 1 μM pepstatin, and 10 μM leupeptin. The homogenates were centrifuged at 12000g for 20 min, and 30μg of protein from the supernatants was then separated on 10% sodium dodecylsulphate−polyacrylamide gel (SDS-PAGE) and transferred to polyvinylidene difluoride membranes. After transfer, the membrane was blocked for 2 h at room temperature with 5% skim milk in Tris-buffered saline-Tween (TBST; 20 mM Tris, 500 mM NaCl, pH 7.5, and 0.1% Tween 20). The membranes were then incubated with mouse monoclonal iNOS or COX-2 (1:1000 dilution) anti-body in 5% skim milk in TBST for 2 h at room temperature. The membranes were washed three times with TBST at room temperature and then incubated with a 1:2000 dilution of antimouse IgG secondary antibody conjugated to horseradish peroxidase (Sigma) in 2.5% skim milk in TBST for 1 h at room temperature. The membranes were washed three times, and the immunoreactive proteins were detected by enhanced chemiluminescence (ECL) using hyperfilm and ECL reagent (Amersham International plc., Buckinghamshire, United Kingdom). The results of Western blot analysis were quantified by measuring the relative intensity compared to the control using Kodak Molecular Imaging Software (Version 4.0.5, Eastman Kodak Company, Rochester, NY) and represented in the relative intensities.

Histological Examination. For histological examination, biopsies of paws were taken 5 h following the interplanetary injection of Carr. The tissue slices were fixed in a solution (1.85% formaldehyde, 1% acetic acid) for 1 week at room temperature, dehydrated by graded ethanol, and embedded in paraffin (Sherwood Medical). Sections (thickness 5μm) were deparaffinized with xylene and stained with hematoxylin and eosin (H&E) stain. All samples were observed and photographed with BH-2 Olympus microscopy. Every 3−5 tissue slices were randomly chosen from Carr, Indo, and imperatorin-treated (10 mg/kg) groups. Histological examination of these tissue slices revealed an excessive inflammatory response with massive infiltration of neutrophils [ploymorphonuclear leukocytes (PMNs)] by microscopy. The numbers of neutrophils were counted in each scope (400×), and thereafter, we obtained their average count from five scopes of every tissue slice.6

Statistical Analysis. Experimental results were presented as the mean± standard deviation (SD) of three parallel measurements. IC50 values were estimated using a nonlinear regression algorithm (SigmaPlot 8.0; SPSS Inc. Chicago, IL). Data obtained from animal experiments were expressed as mean standard error (±SEM). Statistical evaluation was carried out by one-way analysis of variance (ANOVA followed by Scheffe's multiple range tests). Statistical significance is expressed as*p < 0.05, **p < 0.01, and ***p < 0.001.

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RESULTS

Cell Viability and Effect of Imperatorin on

LPS-Induced NO Production in Macrophages. The effect of

imperatorin on RAW264.7 cell viability was determined by a

MTT assay. Cells cultured with imperatorin at the

concen-trations (0, 1, 5, and 10

μg/mL) used in the presence of 100

ng/mL LPS for 24 h did not change cell viability (Figure 1B).

The RAW264.7 cell line is a mouse macrophage cell line used

to model macrophage-mediated inflammatory events in vitro,

and RAW264.7 cells were used to assess the effect of

impe-ratorin on NO synthesis. High levels of NO produced by iNOS

have been defined as a cytotoxic molecule in inflammation.

Imperatorin did not interfere with the reaction between nitrite

and Griess reagents at 10

μg/mL (data not shown).

Unsti-mulated macrophages, after 24 h of incubation in culture

medium, produced background levels of nitrite. When

RAW264.7 macrophages were treated with different

concen-trations of imperatorin (1, 5, and 10

μg/mL) together with LPS

(100 ng/mL) for 24 h, a significant concentration-dependent

inhibition of nitrite production was detected. There was either a

significant decrease in the nitrite production of group treated

with 1

μg/mL imperatorin (p < 0.05) or a highly significant

decrease of groups treated, respectively, with 5 and 10

μg/mL of

imperatorin when compared with the LPS-alone group (p < 0.01

or p < 0.001). The IC

value for inhibition of nitrite production of

imperatorin was about 9.59

± 0.23 μg/mL (Figure 1C).

TNF-

α mediates the production of many other cytokines during

inflammation, in particular the production of interleukin-1

β (IL-1β)

and interleukin-6 (IL-6).

We examined the effect of

imperatorin on LPS induced up-regulation of TNF-

α. A very

low amount of TNF-

α protein was detected by a specific ELISA

for TNF-

α in controls (Figure 1D). When RAW264.7

macro-phages were treated with different concentrations of

impe-ratorin (1, 5, and 10

μg/mL) together with LPS (100 ng/mL)

for 24 h, a significant concentration-dependent inhibition of

TNF-

α production was detected. There was either a significant

decrease in the TNF-

α production of group treated with 1 μg/mL

imperatorin (p < 0.05) or a highly significant decrease of groups

treated, respectively, with 5 and 10

μg/mL of imperatorin when

compared with the LPS-alone group (p < 0.01 or p < 0.001). The

IC

value for inhibition of TNF-

α production of imperatorin was

about 5.32

± 0.12 μg/mL (Figure 1D).

PGE

represents the most important inflammatory product

of COX-2 activity, and it was quantified in cell-free culture

supernatant.

As shown in Figure 1E, cells were stimulated

with LPS alone raise significant amount of PGE

in RAW264.7

macrophages. When RAW264.7 macrophages were treated with

different concentrations of imperatorin (1, 5, and 10

μg/mL)

together with LPS (100 ng/mL) for 24 h, a significant

concentration-dependent inhibition of PGE

production was

detected. The IC

value for inhibition of PGE

production of

imperatorin was about 9.46

± 0.37 μg/mL.

Inhibition of LPS-Induced iNOS and COX-2 Protein by

Imperatorin. To investigate whether the inhibition of NO

production was due to a decreased iNOS and COX-2 protein

level, the effect of imperatorin on iNOS and COX-2 protein

expression was studied by immunoblot. The results showed

that incubation with imperatorin (0, 1, 5, and 10

μg/mL) in the

presence of LPS (100 ng/mL) for 24 h inhibited iNOS and

COX-2 proteins expression in mouse macrophage RAW264.7

cells in a dose-dependent manner (Figure 2A). The detection of

β-actin was also performed in the same blot as an internal control.

The intensity of protein bands was analyzed using Kodak Quantity

software in three independent experiments and showed an average

of 69.2 and 66.7% down-regulation of iNOS and COX-2 proteins,

respectively, after treatment with imperatorin at 10

μg/mL as

compared with the LPS-alone (Figure 2B).

Effects of Imperatorin on Carr-Induced Mice Paw

Edema. Because imperatorin effectively inhibited iNOS and

COX-2 inductions in macrophages, studies were extended to

determine whether imperatorin affected acute phase

inflamma-tion in mice models. In this study, we used Carr-induced edema

because this model is widely employed for screening the effects

of anti-inflammatory drugs. Carr-induced paw edema is shown in

Figure 3A. Imperatorin (10 mg/kg) inhibited (p < 0.001) the

development of paw edema induced by Carr after 4 and 5 h

of treatment, significantly. Indo (10 mg/kg) significantly

decreased the Carr-induced paw edema after 4 and 5 h of

treatment (p < 0.001). On the contrary, imperatorin showed

a good dose

−response activity. Both imperatorin and Indo

show a good reduction of mice paw edema 54.4

± 0.8 and

47.9

± 0.5 inhibition percentage of volume mice paw at the

concentration of 10 mg/kg at 5 h as compared to the control,

respectively.

Effects of Imperatorin on the MDA Level in the Paw

Edema. The MDA level increased significantly in the edema

paw at 5 h after Carr injection (p < 0.001). However, the MDA

level was decreased significantly by treatment with imperatorin

(10 mg/kg) (p < 0.001) as well as 10 mg/kg Indo (Figure 3B).

Effects of Imperatorin on the NO, TNF-

α, and PGE

Levels. In Figure 3C, the NO level increased significantly in

the edema serum at 5 h post-Carr injection (p < 0.001).

Imperatorin (10 mg/kg) significantly decreased the serum NO

level (p < 0.001). The inhibitory potency was similar to that of

Indo (10 mg/kg) at 5 h after induction. TNF-

α and PGE

levels increased significantly in serum at 5 h post-Carr injection

(p < 0.001). However, imperatorin (5 or 10 mg/kg) decreased

the TNF-α and PGE

levels in serum at 5 h after Carr injection

(p < 0.01 or p < 0.001) as well as 10 mg/kg Indo (Figure 3D,E).

Effects of Imperatorin on Activities of Antioxidant

Enzymes. At 5 h after the intrapaw injection of Carr, paw

tissues were also analyzed for the biochemical parameters such

as CAT, SOD, and GPx activities. CAT, SOD, and GPx activities

in paw tissue were decreased significantly by Carr administration.

CAT, SOD, and GPx activities were increased significantly

after treated with 10 mg/kg imperatorin and 10 mg/kg Indo

(P < 0.001) (Table 1).

Effects of Imperatorin on Carr-Induced iNOS and

COX-2 Protein Expressions in Mice Paw Edema. To

investigate whether the inhibition of NO production was due to

a decreased iNOS and COX-2 protein level, the effect of

imper-atorin on iNOS and COX-2 proteins expression was studied by

Western blot. The results showed that injection of imperatorin

(10 mg/kg) on Carr-induced for 5 h inhibited iNOS and COX-2

proteins expression in mouse paw edema (Figure 4A). The

intensity of protein bands was analyzed using Kodak Quantity

software in three independent experiments and showed an

average of 79.8 and 70.3% down-regulation of iNOS and COX-2

protein, respectively, after treatment with imperatorin at 10 mg/kg

as compared with the Carr-induced alone (Figure 4B). In

addition, the protein expression showed an average of 62.1 and

63.2% down-regulation of iNOS and COX-2 protein after

treatment with Indo at 10.0 mg/kg as compared with the

Carr-induced alone. The down-regulation of iNOS and COX-2

activity of the imperatorin (10 mg/kg) was better than Indo

(10.0 mg/kg).

Histological Examination. Paw biopsies of Carr model

animals showed marked cellular infiltration in the connective

tissue. The infiltrates accumulated between collagen fibers and

into intercellular spaces. Paw biopsies of animals treated with

imperatorin (10 mg/kg) showed a reduction in Carr-induced

inflammatory response. Actually, inflammatory cells were

reduced in numbers and were confined to near the vascular

areas. Intercellular spaces did not show any cellular infiltrations.

Collagen fibers were regular in shape and showed a reduction

of intercellular spaces. Moreover, the hypodermal connective

tissue was not damaged (Figure 5A). Neutrophil levels were

significantly increased with Carr treatment (P < 0.01). Indo

(10.0 mg/kg) and imperatorin (10 mg/kg) could decrease

the neutrophils numbers as compared to the Carr-treated group

(P < 0.001) (Figure 5B), significantly.

Figure 2. Inhibition of iNOS and COX-2 protein expression by imperatorin in LPS-stimulated RAW264.7 cells. Cells were incubated for 24 h with 100 ng/mL of LPS in the absence or the presence of imperatorin (0, 1, 5, and 10 μg/mL). Imperatorin was added 1 h before incubation with LPS. Lysed cells were then prepared and subjected to Western blotting using an antibody specific for iNOS and COX-2. β-Actin was used as an internal control. A representative Western blot from two separated experiments is shown. Relative iNOS and COX-2 protein levels were calculated with reference to a LPS-stimulated culture. The data were presented as means± SDs for three different experiments performed in triplicate. ###p < 0.001 control group as compared to the LPS-treated group.*p < 0.05, **p < 0.01, and***p < 0.001 were compared with the LPS-alone group.

■

DISCUSSION

In the present study, we demonstrated anti-inflammatory

activities of imperatorin in in vitro and in vivo experimental

systems, using LPS-stimulated RAW264.7 macrophages and a

mouse model of topical inflammation, respectively. The

inhibitory activities against iNOS and COX-2 as shown in in

vitro assays appear to confer on imperatorin, a potent in vivo

efficacy in mouse, suggesting its potential therapeutic usage as

Figure 3.Effects of imperatorin and Indo on hind paw edema induced by Carr in mice (A), the tissue MDA concentration of foot in mice (B), Carr-induced NO (C), TNF-α (D), and PGE2(E) concentrations of serum at 5 h in mice. Each value represents a mean± SEM.###p < 0.001 as compared with the control group.*p < 0.05, **p < 0.01, and ***p < 0.001 as compared with the Carr group (one-way ANOVA followed by Scheffe's multiple range test).

an anti-inflammatory source of health food. LPS is a

prototypical endotoxin derived from Gram-negative bacterial

membrane and is the initial stimulus leading to induction of

septic shock syndrome. LPS can directly activate macrophages,

endothelial cells, and the complement-triggering production of

inflammatory mediators, such as NO, TNF-

α, interleukins, and

leukotrienes.

However, few reports have been issued on the

anti-inflammatory effect of imperatorin and the mode of action

involved. Thus, this study aimed to evaluate the

anti-inflammatory effect of imperatorin by screening the effects of

imperatorin on LPS-induced pro-inflammatory molecules in

vitro and on acute phase inflammation in vivo.

All furanocoumarins, including byakangelicol, oxypeucedanin, and

isoimperatorin, had no effects on the inhibition of NO production.

Table 1. Effects of Imperatorin and Indomethacin (Indo) on

Changes in CAT, SOD, and GPx Activities Were Studied on

Carr-Induced Mice Paw Edema (5 h)

groups CAT (U/mg protein) SOD (U/mg protein) GPx (U/mg protein) control 5.28± 0.22 24.38± 0.31 23.42± 0.13 Carr 3.58± 0.31 15.64± 0.28 15.86± 0.19 Carr + Indo 4.73± 0.23** 22.53± 0.58** 21.52± 0.21** Carr + imperatorin (1 mg/kg) 3.83± 0.28* 17.23± 0.45* 16.98± 0.26 Carr + imperatorin (5 mg/kg) 4.37± 0.24** 19.82± 0.35** 18.57± 0.39* Carr + imperatorin (10 mg/kg) 4.98± 0.48*** 22.93± 0.63** 21.83± 0.24**

a_{Each value represents a mean± SEM. *p < 0.05, **p < 0.01, and}

***p < 0.001 as compared with the Carr group (one-way ANOVA followed by Scheffe's multiple range test).

Figure 4.Inhibition of iNOS and COX-2 (A) protein expression by imperatorin induced by Carr in the foot at 5 h in mice. Suspended tissue were then prepared and subjected to Western blotting using an antibody specific for iNOS and COX-2.β-Actin was used as an internal control. A representative Western blot from two separated experi-ments is shown. Relative iNOS and COX-2 (B) protein levels were calculated with reference to a Carr-injected mouse. The data were presented as means± SDs for three different experiments performed in triplicate. ###p < 0.001 as compared with the control group. *p < 0.05, **p < 0.01, and ***p < 0.001 as compared with the Carr group (one-way ANOVA followed by Scheffe's multiple range test).

Figure 5. Representative light micrographs of mouse hind footpad H&E stained to reveal hemorrhage, edema, and inflammatory cell infiltration in (A) control mice, (B) Carr-treated mice demonstrat-ing hemorrhage with moderately extravascular red blood cells and a large amount of inflammatory leukocyte mainly neutrophils infiltration in the subdermis interstitial tissue of mice, and (C) mice given Indo (10 mg/kg) before Carr. Imperatorin (10 mg/kg) significantly shows (D) morphological alterations (100×) and (E) the numbers of neu-trophils in each scope (400×) as compared to subcutaneous injection of Carr only.###p < 0.001 control group as compared to the Carr group. ***p < 0.001 as compared with the Carr group. Scale bar = 200 μm.

Our study was performed using equally diluted fractions in

these conditions; the results indicate that imperatorin had

effects on the inhibition of NO production, and imperatorin

and phellopterin rather than byakangelicol, oxypeucedanin,

and isoimperatorin were the two major compounds responsible

for the anti-inflammatory activity in the Angelica dahurica.

The anti-inflammatory properties of methylene chloride

fraction from G. littoralis extract (MCF-GLE) may result

from the inhibition of pro-inflammatory mediators, such as

NO, PGE

, TNF-α, and IL-1β, via suppression of nuclear

factor-

κB (NF-κB) and mitogen-activated protein

kinase-dependent pathways.

Excessive production of NO plays a critical role in the

aggravation of circulatory shock and chronic inflammatory

diseases, such as septic shock, inflammatory hepatic

dysfunc-tions, inflammatory lung disease, and colitis.

As many of these

conditions exhibit rapid onset and development, often resulting

in the failure of conventional anti-inflammatory therapies and

extremely high mortality rates, a simultaneous suppression of

NO production pathways, as shown by imperatorin, may satisfy

the so far unmet need for control of the rapid progression of

the inflammatory process. In vitro models such as macrophage

cells or other cell lines are useful materials with a steady

high-level production of NO. The mechanisms by which imperatorin

inhibits macrophage functions have not been elucidated.

Results in vitro showed that imperatorin suppressed

LPS-induced production of NO (Figure 1C), the expression of

inflam-matory protein products such as iNOS and COX-2 (Figure 2A).

Examination of the cytotoxicity of imperatorin in RAW264.7

macrophages using MTT assay has indicated that imperatorin

even at 10

μg/mL did not affect the viability of RAW264.7 cells.

Therefore, inhibition of LPS-induced nitrite production by

imperatorin was not the result of a possible cytotoxic effect on

these cells.

Excess amounts of NO and PGE

play a critical role in the

aggravation of chronic inflammatory diseases, such as hepatic

dysfunction and pulmonary disease. Recently, mounting

ev-idence that in vitro and in vivo have indicated existing cross-talk

between the release of NO and prostaglandins (PGs) in the

modulation of molecular mechanisms that regulate PGs

generat-ing pathway.

Scientific papers observed that while the

produc-tion of both nitrite and PGE

was blocked by the NOS inhibitors

in mouse macrophages RAW264.7 cells, these inhibitory effects

were reversed by coincubation with the precursor of NO

syn-thesis,

-arginine. Furthermore, inhibition of iNOS activity by

nonselective NOS inhibitors attenuated the release of NO and

PGs simultaneously in LPS-activated macrophages, suggesting

that endogenously released NO from macrophages exerted a

stimulatory action on enhancing the PGs production.

Con-versely, it has been shown that COX activation in turn modulates

the

-arginine-NO pathway, whereas COX inhibition decreases

NOS activity in human platelets.

These results are indicative of

the cross-talk between NO and PGs pathways.

Carr-induced paw edema is a well-established model of

edema formation, which is commonly used for the screening of

anti-inflammatory drugs. The intraplantar injection of Carr

induces inflammatory responses, including increases in paw

volume (edema) and neutrophil infiltration.

Recent studies have

shown that Carr induced peripheral release of NO as well as that

of PGE

.

NO plays a major role in edema formation in

inflam-matory responses and tissue injury, and Carr induced the release

of TNF-

α, which subsequently promotes IL-1 and IL-6 production

in the tissue.

The degree of swelling of the Carr-injected paws

was maximal 3 h after injection. Statistical analysis revealed that

imperatorin and Indo significantly inhibited the development of

edema 5 h after treatment (p < 0.001) (Figure 3A). The third

phase of the edema-induced by Carr, where the edema reaches

its highest volume, is characterized by the presence of

prosta-glandins and other compounds of slow reaction.

It was found

that the injection of Carr into the mouse paw induces the

liberation of bradykinin, which later induces the biosynthesis of

prostaglandin and other autacoids, which are responsible for the

formation of the inflammatory exudates.

Our Carr-induced

rat paw edema model enabled us to demonstrate the ability of

imperatorin to inhibit edema induced by acute inflammation.

These results in conjunction with the marked inhibition of

LPS-induced NO and TNF-

α productions by imperatorin in

macrophages imply that the antiedema effects of imperatorin

might result from its inhibition of NO and TNF-

α syntheses in

the peripheral tissues (Figure 3C,D).

The proinflammatory cytokines such as TNF-

α and IL-1β are

small secreted proteins, which mediate and regulate immunity

and inflammation. The production of TNF-

α is crucial for the

synergistic induction of NO synthesis in interferon-γ (IFN-γ)

and/or LPS-stimulated macrophages. TNF-

α induces a number

of physiological effects including septic shock, inflammation,

and cytotoxicity.

Also, TNF-

α is a mediator of Carr-induced

inflammatory incapacitation and is able to induce the further

release of kinins and leukotrienes, which is suggested to have an

important role in the maintenance of long-lasting nociceptive

response.

In this study, we found that imperatorin decreased

the TNF-

α level in LPS-stimulated macrophages or after Carr

injection.

The Carr-induced inflammatory response has been linked to

neutrophils infiltration and the production of

neutrophils-derived free radicals, such as hydrogen peroxide, superoxide,

and hydroxyl radicals, as well as the release of other

neutrophils-derived mediators.

Researchers demonstrated that the

inflam-matory effect induced by Carr is associated with free radical. Free

radical, prostaglandin, and NO will be released when

adminis-trating with Carr for 1

−6 h. MDA production is due to free

radical attack plasma membrane. Thus, the inflammatory effect

would result in the accumulation of MDA.

Glutathione (GSH)

acts as a scavenger by scavenging NO and other oxidants. The

increased GSH level may favor reduction in MDA production.

GSH plays an important role against Carr-induced local

inflammation.

In this study, there was significantly increased

in CAT, SOD, and GPx activities with imperatorin treatment

(Table 1). Furthermore, there were significant decreases in the

MDA level with imperatorin treatment (Figure 3B). We assume

that the suppression of MDA production is probably due to the

increases of CAT, SOD, and GPx activities.

In conclusion, these results suggested that imperatorin

pos-sessed anti-inflammatory effects. The anti-inflammatory

mech-anism of imperatorin may be related to iNOS and COX-2, and

it is associated with the increase in the activities of antioxidant

enzymes (CAT, SOD, and GPx). Imperatorin may be used as a

pharmacological agent in the prevention or treatment of disease

in which free radical formation is a pathogenic factor.

■

AUTHOR INFORMATION

Corresponding Author

*Tel: +886 4 2207-1693. Fax: +886 4 2207-1693. E-mail: kuoyh@

mail.cmu.edu.tw.

Author Contributions

+

These authors equally contributed to this work.

Funding

We are thankful for the financial support from the National

Science Council (NSC100-2313-B-039-004- and NSC

100-2320-B-039-033-), China Medical University (CMU) (CMU99-S-29,

CCM-P99-RD-042, and CMU99-COL-10), and Taiwan

Depart-ment of Heath Clinical Trial and Research Center of Excellence

(DOH101-TD-B-111-004).

■

ACKNOWLEDGMENTS

We thank Dr. Jeffrey Conrad for critically reading the

manuscript.

■

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