Analgesic Effect of the Newly Developed S(+)-Flurbiprofen Plaster on Inflammatory Pain in a Rat Adjuvant-Induced Arthritis Model.

Preclinical Research This article describes the properties of a novel topical NSAID (Nonsteroidal anti-inflammatory drug) patch, SFPP (S(+)-flurbiprofen plaster), containing the potent cyclooxygenase (COX) inhibitor, S(+)-flurbiprofen (SFP). The present studies were conducted to confirm human COX inhibition and absorption of SFP and to evaluate the analgesic efficacy of SFPP in a rat adjuvant-induced arthritis (AIA) model. COX inhibition by SFP, ketoprofen and loxoprofen was evaluated using human recombinant COX proteins. Absorption of SFPP, ketoprofen and loxoprofen from patches through rat skin was assessed 24 h after application. The AIA model was induced by injecting Mycobacterium tuberculosis followed 20 days later by the evaluation of the prostaglandin PGE2 content of the inflamed paw and the pain threshold. SFP exhibited more potent inhibitory activity against COX-1 (IC50 = 8.97 nM) and COX-2 (IC50 = 2.94 nM) than the other NSAIDs evaluated. Absorption of SFP was 92.9%, greater than that of ketoprofen and loxoprofen from their respective patches. Application of SFPP decreased PGE2 content from 15 min to 6 h and reduced paw hyperalgesia compared with the control, ketoprofen and loxoprofen patches. SFPP showed analgesic efficacy, and was superior to the ketoprofen and loxoprofen patches, which could be through the potent COX inhibitory activity of SFP and greater skin absorption. The results suggested SFPP can be expected to exert analgesic effect clinically.

Effects of combined treatment with eldecalcitol and alendronate on bone mass, mechanical properties, and bone histomorphometry in ovariectomized rats: a comparison with alfacalcidol and alendronate.

Eldecalcitol (ELD), a 2ß-hydroxypropyloxy derivative of 1α,25 (OH) 2D3, inhibits bone resorption more potently than alfacalcidol (ALF) while maintaining osteoblastic function in an ovariectomized (OVX) osteoporosis rat model. Alendronate (ALN), which is the most common bisphosphonate used for the treatment of osteoporosis, increases the bone mineral density (BMD) by suppressing bone resorption. In this study, we investigated the effects of combination treatments with ELD and ALN or with ALF and ALN on bone mass and strength in OVX rats. Seventy female rats, 32 weeks old, were assigned to seven groups: (1) a sham-operated control group; (2) an OVX-control group; (3) an ELD group; (4) an ALF group; (5) an ALN group; (6) an ELD+ALN group; and (7) an ALF+ALN group. OVX rats were orally treated with ELD (0.015 µg/kg), ALF (0.0375 µg/kg), or ALN (0.2mg/kg) daily for 12 weeks. In both the lumbar spine and the femur, ELD and ALF monotherapy significantly increased the BMD, and ELD+ALN and ALF+ALN significantly increased the BMD, compared with ALN monotherapy, as an additive effect. In particular, ELD+ALN resulted in a significantly higher BMD than ALF+ALN in the femur. On mechanical testing of the lumbar spine, ELD and ALF monotherapy significantly increased the ultimate load, and ELD+ALN and ALF+ALN significantly increased the ultimate load compared with ALN monotherapy. In the femur, ELD, ELD+ALN, and ALF+ALN treatment significantly increased the ultimate load, compared with the OVX-control group, and ELD+ALN resulted in a significantly higher ultimate load than ALN monotherapy. A histomorphometric analysis showed that ELD monotherapy and ELD+ALN combination therapy had a potent inhibitory effect on bone resorption parameters (osteoclast surface and eroded surface), while maintaining bone formation parameters (osteoblast surface and osteoid surface). By contrast, ALF and ALF+ALN significantly lowered the histological parameters of both bone resorption and formation. These results suggested that ELD or ALF used in combination with ALN has therapeutic advantages over ALN monotherapy, with ELD+ALN combination treatment producing an especially beneficial anti-osteoporotic effect by inhibiting osteoclastic bone resorption and maintaining osteoblastic function, compared with ALF+ALN combination treatment.

Itch-associated scratching contributes to the development of dermatitis and hyperimmunoglobulinaemia E in NC/Nga mice.

Atopic dermatitis (AD) is related to immunoglobulin E (IgE) production, and a type-1 and type-2 helper T cell (Th1/Th2) imbalance has been hypothesized as the aetiology. While itching and scratching are important factors in the development of dermatitis, the mechanisms underlying these phenomena are poorly understood. We investigated the relationship between scratching, transepidermal water loss (TEWL), signs of dermatitis and serum Ig levels in NC/Nga mice, a model of AD. We also sensitized specific pathogen-free (SPF)-NC/Nga mice and BALB/c mice to mite antigen to determine the effects of IgE overproduction on scratching and investigated the involvement of mast cells and T/B cells in the induction of scratching using WBB6F1-W/W(v) mice and C.B.17/Icr-scid mice. Under conventional conditions, the scratch counts increased, followed by increases in TEWL and the inflammation score in NC/Nga mice that were not kept under SPF conditions. However, no change was observed in scratching, TEWL, or signs of dermatitis in mite antigen-sensitized SPF-NC/Nga and BALB/c mice, although the serum total IgE, IgG(1) and IgG(2a) levels increased. The scratch count increased significantly in both the WBB6F1-W/W(v) mice and C.B.17/Icr-scid mice when they were co-housed with skin-lesioned NC/Nga mice, raised under conventional conditions. These results show that IgE overproduction results from itch-associated scratching-induced dermatitis in NC/Nga mice.

High levels of human recombinant cyclooxygenase-1 expression in mammalian cells using a novel gene amplification method.

We report the expression of a high level of human cyclooxygenase-1 (hCOX-1) in mammalian cells using a novel gene amplification method known as the IR/MAR gene amplification system. IR/MAR-plasmids contain a mammalian replication initiation region (IR) and a nuclear matrix attachment region (MAR) and amplify autonomously without a specific induction process. In this study, the IR/MAR-plasmid pΔBN.AR1 was cotransfected with pCAG-COX1, which expresses hCOX-1, into human HEK293T cells, and G418 and blasticidin S double-resistant cells were obtained in about 1month. Real-time PCR and Western blotting revealed that the expressions of hCOX-1 mRNA and protein in both polyclonal and monoclonal cells were remarkably higher than those in only pCAG-COX1-transfected control cells. Southern blotting demonstrated the amplification of the hCOX-1 gene, and the copy number of clone #43 obtained by the cotransfection of pΔBN.AR1 and pCAG-COX1 was more than 20 copies per cell, though that of clone #14 obtained without using the IR/MAR plasmid pΔBN.AR1 was only two copies. These results indicate that a high level of hCOX-1 expression was achieved as a result of hCOX-1 gene amplification. Furthermore, the crude extract from clone #43 showed a strong COX-1 activity, and the activity was inhibited by the representative COX-1 inhibitor indomethacin, with an IC(50) value of 36nM. These results demonstrate that the IR/MAR gene amplification system is a simple but useful method for generating highly productive mammalian cells.

The importance of brain PGE2 inhibition versus paw PGE2 inhibition as a mechanism for the separation of analgesic and antipyretic effects of lornoxicam in rats with paw inflammation.

OBJECTIVES: Lornoxicam is a non-selective cyclooxygenase inhibitor that exhibits strong analgesic and anti-inflammatory effects but a weak antipyretic effect in rat models. Our aim was to investigate the mechanism of separation of potencies or analgesic and antipyretic effects of lornoxicam in relation to its effect on prostaglandin E2 (PGE2) production in the inflammatory paw and the brain. METHODS: A model of acute or chronic paw inflammation was induced by Freund's complete adjuvant injection into the rat paw. Lornoxicam (0.01-1 mg/kg), celecoxib (0.3-30 mg/kg) or loxoprofen (0.3-30 mg/kg) was administered orally to the rats and the analgesic and antipyretic effects were compared. The paw hyperalgesia was assessed using the Randall-Selitto test or the flexion test. Dorsal subcutaneous body temperature was measured as indicator of pyresis. After the measurement of activities, the rats were sacrificed and the PGE2 content in the paw exudate, cerebrospinal fluid or brain hypothalamus was measured by enzyme-immunoassay. KEY FINDINGS: In a chronic model of arthritis, lornoxicam, celecoxib and loxoprofen reduced hyperalgesia with an effective dose that provides 50% inhibition (ED50) of 0.083, 3.9 and 4.3 mg/kg respectively, whereas the effective dose of these drugs in pyresis was 0.58, 0.31 and 0.71 mg/kg respectively. These drugs significantly reduced the PGE2 level in paw exudate and the cerebrospinal fluid. In acute oedematous rats, lornoxicam 0.16 mg/kg, celecoxib 4 mg/kg and loxoprofen 2.4 mg/kg significantly reduced hyperalgesia to a similar extent. On the other hand, lornoxicam did not affect the elevated body temperature, whereas celecoxib and loxoprofen significantly reduced the pyrexia to almost the normal level. These drugs significantly reduced the PGE2 level in inflamed paw exudate lo almost the normal level. On the other hand, lornoxicam did not change PGE2 level in the brain hypothalamus, whereas celecoxib and loxoprofen strongly decreased it. CONCLUSIONS: Lornoxicam exhibits strong analgesic but weak antipyretic effects in rats with paw inflammation. Such a separation of effects is related to its efficacy in the reduction of PGE2 levels in the paw and brain hypothalamus.

Imine derivatives as new potent and selective CB2 cannabinoid receptor agonists with an analgesic action.

In this study, a novel series of CB(2) receptor agonist imine derivatives, 1-6, was synthesized and evaluated for activity against the CB(2) receptor. In a previous paper we reported the synthesis and SARs of thiazole derivative 1, a potent CB(2) receptor agonist, but we had not assessed chemical modifications of the 5-membered heteroring of 1. In the present study, we therefore tried chemically modifying the 5-membered heteroring of 1 in an attempt to further improve binding affinity for the CB(2) receptor. In the course of making the structural modifications, we discovered that a novel pyrazole derivative 6b (CBS0550) had high affinity for the CB(2) receptor (IC(50)=2.9 nM, EC(50)=1.8 nM, E(max)=85%), high selectivity for CB(2) (CB(1) IC(50)/CB(2) IC(50)=1400), and good physicochemical properties (solubility in water: 5.9 mg/100mL at 25 degrees C). Oral administration of 6b to rats at a dose of 10mg/kg resulted in significant plasma concentrations, and orally administered compound 6b significantly reversed mechanical hyperalgesia in the Randall-Selitto model of inflammatory pain in rats.

Modulation of scratching behavior by silencing an endogenous cyclooxygenase-1 gene in the skin through the administration of siRNA.

BACKGROUND: RNA interference (RNAi) is rapidly becoming a major tool that is revolutionizing research in the bioscience and biomedical fields. To apply the RNAi technique in vivo, it is crucial to develop appropriate methods of guiding the short interfering RNA (siRNA) molecules to the right tissues and cells. Here, we demonstrate an efficient method for performing gene knockdown in the body skin using the in vivo electro-transduction of siRNA. Using this method, we examined whether the targeted silencing of the cyclooxygenase (COX) gene in the skin could modulate the scratching behavior of an atopic dermatitis mouse model. METHODS: NC/Nga mice were used as the atopic dermatitis model. Using our optimized in vivo electroporation conditions, siRNAs were introduced into the skin; the silencing efficiency was then analyzed by Western blotting, measuring the levels of prostaglandins, and immunohistochemistry. The scratching behaviors of the mice were measured using an automatic system. RESULTS: Targeted silencing of the COX-1 gene using our in vivo siRNA technique significantly accelerated the scratching behavior of NC/Nga mice, whereas the COX-2 siRNA showed no effect. In addition, the effect of COX-1 siRNA was mimicked by treatment with a COX-1-selective inhibitor (SC-560). CONCLUSIONS: We have demonstrated the successful silencing of endogenous gene expression in the skin using the intradermal transfection of unmodified siRNA via electroporation. Using this method, we revealed that COX- 1-mediated prostaglandins may act as endogenous inhibitors of scratching behavior.

The anti-pruritic efficacy of TS-022, a prostanoid DP1 receptor agonist, is dependent on the endogenous prostaglandin D2 level in the skin of NC/Nga mice.

TS-022 is a prostanoid DP(1) receptor agonist, originally developed as a novel anti-pruritic drug for atopic dermatitis. The drug has been shown to suppress scratching and improve the skin inflammation in the NC/Nga (NC) mouse, a model of atopic dermatitis. Corticosteroids are commonly used as effective agents for the treatment of atopic dermatitis. We examined the anti-pruritic efficacy of TS-022 in NC mice cohabited with skin-lesioned NC mice, which showed spontaneous scratching without skin lesions in the early phase and chronic itching with severe dermatitis in the late phase, in comparison with that of dexamethasone. We have previously reported that prostaglandin D(2) might have a physiological role in the inhibition of pruritus. While after 2 weeks of cohabitation with skin-lesioned NC mice (early phase of dermatitis, characterized by the appearance of spontaneous scratching), topically applied TS-022 exhibited a weak anti-pruritic effect in the NC mice, after 6 weeks of cohabitation (late phase, characterized by both chronic scratching and dermatitis), the drug exerted potent anti-pruritic activity. In contrast, dexamethasone exerted potent anti-pruritic effect in both the early and late phases. Indomethacin aggravated the scratching in the early phase, but had no effect in the late phase. The skin prostaglandin D(2) level was significantly increased in the early phase, to subsequently declined and return to the basal level in the late phase. The cutaneous ability for prostaglandin D(2) production following topical application of arachidonic acid or mechanical scratching was decreased in the late phase. Moreover, the expression level of the prostanoid DP(1) receptor in the skin was increased in the late phase. These findings suggest that the potent anti-pruritic activity of TS-022 in the late phase might be attributable to the decrease of endogenous prostaglandin D(2) production and increase of prostanoid DP(1) receptor expression.

Role of scratch-induced cutaneous prostaglandin D production on atopic-like scratching behaviour in mice.

NC/Nga mice are known to develop scratching dermatitis akin to atopic dermatitis, under conventional (Conv), but not under the specific-pathogen-free (SPF) condition. In this study, we examined the effects of mechanical-scratching on the spontaneous scratching counts (sign of itching), in relation to the cutaneous prostaglandin D2 (PGD2) levels in NC/Nga or BALB/c mice. Mechanical-scratching increased the cutaneous barrier damage and PGD2 levels in both strain mice under the SPF condition. By 4 weeks of cohabitation with the skin-lesioned NC/Nga mice, both the increase in the spontaneous scratching and development of dermatitis score were higher in the Conv-NC/Nga than in the Conv-BALB/c mice. At this time-point, the cutaneous PGD2 level induced by mechanical-scratching was significantly lower in the Conv-NC/Nga when compared with that in the SPF-NC/Nga mice, and that in the Conv-BALB/c was almost equal to that in the SPF-BALB/c mice. With mechanical scratches, the cohabitation-induced scratching was suppressed in the Conv-BALB/c, but not in the Conv-NC/Nga mice. These results suggest that the scratch-induced cutaneous PGD2 inhibits scratching and the subsequent development of dermatitis in BALB/c, while the impaired scratch-induced cutaneous PGD2 production in the NC/Nga mice resulted in no suppression of scratching, and aggravated the dermatitis.

Putative mechanism of the itch-scratch circle: repeated scratching decreases the cutaneous level of prostaglandin D2, a mediator that inhibits itching.

In atopic dermatitis, scratching of the skin as a reaction to itching causes injury to the skin, which, in turn, further increases the itching resulting in the establishment of the so-called itch-scratch circle. We have shown that prostaglandin (PG) D2 plays an inhibitory role against pruritus in mice with atopic-like dermatitis; therefore, we examined the relationship between scratching and the cutaneous PGD2 level using an artificial scratching model with a wire brush. Mechanical scratching induced a temporary increase of the skin PGs levels (PGE2, PGD2, 6-ketoPGF1alpha, PGF2alpha). The skin PGD2 level and the ability of PGD2 production decreased at 48 h after repeated scratch, compared to that of normal skin, not so after single scratch. Immunohistochemical analysis and Western blotting revealed a decrease in the levels of cyclooxygenase-1 (COX-1) and hematopoietic PGD synthase in mechanically scratched skin. The reduced ability of the skin for PGD2 production following mechanical scratching could be caused by this decrease in the expression levels of COX-1 and PGD2 synthase. The results suggest that repeated scratching in mice decreases the ability of the skin to produce PGD2, which is an endogenous mediator that inhibits pruritus, resulting in the establishment of the itch-scratch circle.

Effects of TS-022, a newly developed prostanoid DP1 receptor agonist, on experimental pruritus, cutaneous barrier disruptions and atopic dermatitis in mice.

TS-022, {4-[(1R, 2S, 3R, 5R)-5-Chloro-2-((S)-3-cyclohexyl-3-hydroxyprop-1-ynyl)-3-hydroxycyclopentyl] butylthio} acetic acid monohydrate, inhibits ADP-induced platelet aggregation, an effect significantly antagonized, as in the case of prostaglandin D(2) by the prostanoid DP(1) receptor antagonist (BW A868C). TS-022 is a prostanoid DP(1) receptor agonist, originally developed as a novel anti-pruritic drug for patients with atopic dermatitis. We examined the effects of TS-022 on experimental pruritus, cutaneous barrier disruption, and atopic dermatitis and in in vitro immune function tests. Topically applied TS-022 significantly suppressed scratching in skin-lesioned NC/Nga mice from a concentration of 2.5 nM, and this scratch-suppressive activity was significantly antagonized by BW A868C. Tacrolimus (FK-506) and dexamethasone, used as reference drugs for atopic dermatitis, also exhibited suppressive effects against scratching, but only at concentrations of 125 and 25,000 microM. TS-022 applied topically, once a day for 2 days, significantly accelerated repair of the cutaneous barrier disruption caused by mechanical scratching, from concentrations of 2.5 nM. This acceleration of repair of the disrupted cutaneous barrier by this drug was also significantly antagonized by BW A868C. FK-506 and dexamethasone showed no beneficial effects on the repair of the disrupted cutaneous barrier. Repeated topical application of 2.5 microM of TS-022 and 12.5 microM of FK-506 once a day for 6 weeks significantly improved the skin inflammation scores in the NC/Nga mice. In regard to the effects of TS-022 in vitro, the inhibitory activity of TS-022 against concanavalin A-induced cytokine production by splenocytes was marginal as compared with that of FK-506 or dexamethasone. These results suggest that the beneficial therapeutic effects of TS-022 in NC/Nga mice with atopic dermatitis are mediated by its suppressive effect on scratching and its effect of accelerating repair of the disrupted cutaneous barrier, both effects being attributable to its prostanoid DP(1) receptor agonistic activity.

Time course changes of scratching counts, dermatitis symptoms, and levels of cutaneous prostaglandins in NC/Nga mice.

NC/Nga (NC) mice are known to develop dermatitis resembling atopic dermatitis (AD) in conventional (Conv) conditions, but not in specific pathogen-free (SPF) conditions. We reported that the ability of skin prostaglandin D(2) (PGD(2)) production, which might be the endogenous inhibitor of itching, was attenuated in skin-lesioned Conv-NC mice. We examined the age-related change in scratching, dermatitis symptoms, and skin PGs of SPF- and Conv-NC mice. In Conv-NC, PGD(2) increased at 7 weeks, at which scratching counts increased, but dermatitis did not develop. PGE(2), PGI(2) and PGF(2alpha) increased at 10 and 13 weeks, at which dermatitis developed. The ability to produce skin PGs was examined by measuring PGs after application of arachidonic acid or after mechanical scratching using a wire brush. In Conv-NC, PGD(2) production at 13 weeks was lower than at 7 weeks. In Conv-NC, hematopoietic PGD synthase (hPGDS) expression in the skin at 13 weeks was lower than at 7 weeks by Western blotting and immunohistochemical analysis. The increase of skin PGD(2) level in the early phase of the development of dermatitis is due to the stress of extensive scratching, but did not increase in spite of the stress of extensive scratching in the late phase, due to decreasing capacity of PGD(2) production attributable to decreasing hPGDS expression in Conv-NC mice. These results suggest that a decreased ability to produce skin PGD(2) production could enhance scratching and aggravate dermatitis in Conv-NC mice.

COX-1 inhibition enhances scratching behaviour in NC/Nga mice with atopic dermatitis.

NC/Nga (NC) mice, spontaneously develop an eczematous atopic dermatitis (AD)-like skin lesion when kept under conventional condition (Conv), but not under specific pathogen-free (SPF) conditions, have been thought to be an animal model of AD. We have previously shown that PGD(2) and arachidonic acid inhibited the scratching behaviour of NC mice, while indomethacin enhanced it. This study was designed to assess the role of cyclooxygenase (COX)-1 and COX-2 in the itch-related scratching behaviour of NC mice. We examined the expression of COX in the skin using real-time PCR and Western blotting and the effects of SC-560 (a COX-1 selective inhibitor) or NS-398 (a COX-2 selective inhibitor) on scratching behaviour in relation to skin prostaglandin (PG) levels in NC mice. COX-1 mRNA expression was unchanged and protein expression decreased in Conv NC mice compared with that of SPF mice. By contrast, COX-2 mRNA and protein expression increased in Conv NC mice. SC-560 increased scratching behaviour and significantly reduced skin PGD(2), PGE(2) and PGF(2alpha) levels, but NS-398 did not have effects on scratching and skin PG level. Moreover, the topical application of PGD(2), which might be the endogenous inhibitor of itching, suppressed the SC-560-induced enhancement of scratching behaviour by NC mice. These results suggest COX-1-coupled skin PGD(2) biosynthesis plays a physiological role in inhibiting regulation of pruritus in NC mice with AD.

Effects of indomethacin and dexamethasone on mechanical scratching-induced cutaneous barrier disruption in mice.

Effects of indomethacin and dexamethasone on recovery of cutaneous barrier disruption induced by mechanical scratching were examined. Cutaneous barrier was disrupted by scratching using a stainless-steel wire brush (mechanical scratching) and compared to cutaneous application of acetone/ether (1:1) mixture (AE) and tape-stripping. Increase of transepidermal water loss (TEWL), as an indicator of a broken skin barrier, and recovery period for mechanical scratching were higher and longer than those for AE treatment and tape-stripping and we also confirmed the severity of skin damage in a histological study. Topical application of moisturizers showed a temporal effect, rapidly decreased TEWL on mechanical scratching- or AE treatment-induced cutaneous barrier disruption, and gradually increased base levels from 4 to 12 h after treatment. Topical application of indomethacin or dexamethasone prolonged the recovery period for the cutaneous barrier, and concomitant use further worsened the status of the barrier. Additionally, we examined the effects of prostaglandins (PGs) and inflammatory cytokine on mechanical scratching-induced cutaneous barrier disruption pretreated with indomethacin and dexamethasone. As a results, PGD2 and interleukin (IL)-1beta significantly accelerated the recovery of cutaneous barrier disruption by mechanical scratching but such was not the case with PGE2, IL-1alpha, and tumor necrosis factor-alpha treatment. These results suggest that indomethacin and dexamethasone prolonged the recovery period caused by inhibition of PGD2 and IL-1beta. Mechanical scratching-induced cutaneous barrier disruption may be a useful method for evaluating means of recovery from skin damage.

Prostaglandin D2 and prostaglandin E2 accelerate the recovery of cutaneous barrier disruption induced by mechanical scratching in mice.

The role of prostaglandins in mechanical scratching-induced cutaneous barrier disruption in mice was investigated. Skin prostaglandins contents were measured after cutaneous barrier function was disrupted by scratching using a stainless-steal wire brush (mechanical scratching), then effects of prostanoids on recovery of cutaneous barrier functions were examined. This mechanical scratching increased transepidermal water loss and skin prostaglandins (prostaglandin D2, prostaglandin E2, 6-keto-prostaglandin F1alpha and prostaglandin F2alpha) contents, count-dependently. Topical application of indomethacin immediately after cutaneous barrier disruption delayed the recovery period of cutaneous barrier disruption. We examined effects of several prostanoids (prostaglandin D2, prostaglandin E2, prostaglandin F2alpha, prostaglandin I2 and U46619) on delay of the recovery process of mechanical scratching-induced cutaneous barrier disruption with treatment of indomethacin. Topically applied prostaglandin D2 and prostaglandin E2 accelerated the recovery of cutaneous barrier disruption and topical application of prostaglandin J2, limaprost, sulprostone and ONO-4819, but not 13,14-dihydro-15-keto-prostaglandin D2, 15-deoxy-Delta(12,14)-prostaglandin J2, 17-phenyl-trinor-prostaglandin E2 or butaprost had effects on recovery of the cutaneous barrier. These results suggest that prostaglandin D2 and prostaglandin E2 accelerate the recovery process of cutaneous barrier disruption caused by mechanical scratching, via specific prostanoid DP1, EP3 and EP4 receptors.

Prostanoid DP1 receptor agonist inhibits the pruritic activity in NC/Nga mice with atopic dermatitis.

NC/Nga mice have similar pathological and behavioral features of human atopic dermatitis and are used as a model of the disease. Under conventional circumstances, spontaneous and persistent scratching is frequent and can lead to the onset of skin inflammation. We examined the effects of several prostanoids and their related compounds on the scratching behavior of NC/Nga mice. Among them, topically applied prostaglandin D2, prostaglandin E1, prostaglandin E2 and prostaglandin I2 significantly suppressed the scratching, the order of inhibitory activities being prostaglandin D2>>prostaglandin I2>prostaglandin E1=prostaglandin E2. Prostaglandin D2 metabolite, prostaglandin J2 also significantly suppressed the scratching but not so 13,14-dihydro-15-keto-prostaglandin D2, and 15-deoxy-Delta12,14-prostaglandin J2. The order of the inhibitory activities of these prostaglandin D2 metabolites depended on affinity of the prostanoid DP1 receptor but not on the DP2 receptor (chemoattractant receptor-homologous molecule expressed on T helper2 cells, CRTH2) and PPAR-gamma receptors. Likewise, topically applied arachidonic acid significantly suppressed the scratching while indomethacin enhanced it. Pretreatment of arachidonic acid increased the skin prostaglandins (prostaglandin D2, prostaglandin E2, prostaglandin F2alpha and 6-keto-prostaglandin F1alpha) contents, but indomethacin decreased the prostaglandin D2 and prostaglandin E2 contents. On the other hand, prostaglandin D2 and indomethacin had no apparent effects on histamine-induced scratching of ICR mice. These results suggested that prostaglandin D2 plays a physiological role in inhibiting pruritus of NC/Nga mice via their specific prostanoid DP1 receptors, and that prostaglandin D2 and/or a prostanoid DP1 receptor agonist may have therapeutic effects for cases of consecutive skin inflammation.