Ciclamilast ameliorates adjuvant-induced arthritis in a rat model

Abstract

We assessed the effect of a novel and selective phosphodiesterase 4 (PDE4) inhibitor, ciclamilast, on chronic inflammation in adjuvant-induced arthritis (AIA), a rat model of rheumatoid arthritis (RA), and acute inflammation in the rat and mouse model of carrageenan-induced paw edema and peritonitis. Our results showed that daily oral administration of ciclamilast at 1, 3, and 10 mg/kg dose-dependently inhibited the increase in hind paw volume of rats with AIA. The inhibition of paw edema was associated with inhibition of both the production of cytokines such as TNF-α, IL-1β, and IL-6 and cell infiltration assessed in subcutaneous paw tissue. Moreover, there was significantly less tissue destruction in the ciclamilast-treated rats compared to the vehicle-treated rats, as assessed by radiographic analysis and histopathological evaluation. In the two acute inflammation models, ciclamilast inhibited carrageenan-induced paw edema in rats and inflammatory cell migration into the peritoneal cavity in mice in a dose-dependent manner. These results not only suggest that ciclamilast, as a disease-modifying antirheumatic drug (DMARD), can attenuate RA but also provide proof of principle that a PDE4 inhibitor may be useful for the treatment of arthritis.

Figure 1

Anti-inflammatory effect of ciclamilast on AIA in rats. Time course of paw swelling on the contralateral paw and the area under curve (AUC) of paw swelling on the contralateral paw in rats with AIA on day 28. Control (no adjuvant, no treatment); vehicle, 1, 3, and 10 mg/kg ciclamilast (cic) and 0.1 mg/kg MTX were administered by oral gavage. Hind paw volume (mL) was measured before and after drug administration using a water-replacement plethysmometer. All drugs were administered by oral gavage. Statistical analysis was performed by one-way ANOVA (Dunnett's method) or Mann-Whitney t-test. ^### P < 0.001 versus control; ^* P < 0.05, ^** P < 0.01 versus vehicle. Data represent the mean ± S.E.M. (n = 9-10/group).

Figure 2

Radiographic (a) and histopathological images (b) of hind paws from representative rats on day 28. Note the evidence of swelling and tissue damage in the treatment rats compared with the control rats (a). Ciclamilast displayed potent and dose-dependent inhibitory effects on both swelling and bone changes and reduced the average radiographic (c) and histopathological scores (d).

Figure 3

Effect of ciclamilast on body and immune organ weights. The wet weight of organs (spleen and thymus) harvested from rats with adjuvant-induced arthritis on day 28. Statistical analysis was performed by one-way ANOVA (Dunnett's method) or Mann-Whitney t-test. ^# P < 0.05, ^## P < 0.01 versus control; ^* P < 0.05, ^** P < 0.01 versus vehicle rats. Data represent the mean ± S.E.M. (n = 9-10/group).

Figure 4

Effect of ciclamilast on the cytokine levels in paw tissue of rats with AIA. Rats with AIA were treated with vehicle or 1, 3, or 10 mg/kg ciclamilast or 0.1 mg/kg MTX via oral gavage from days 0 to 28 after adjuvant induction. Twenty-four hours after the last administration of ciclamilast, rats were killed. The subcutaneous tissue of the right hind paw and the surrounding tarsotibial joints were removed, homogenized, and used for assessment of cytokine levels by ELISA. Statistical analysis was performed by one-way ANOVA (Dunnett's method) or Mann-Whitney t-test. ^# P < 0.05, ^## P < 0.01 versus control; ^* P < 0.05, ^** P < 0.01 versus vehicle rats. Data represent the mean ± S.E.M. (n = 9-10/group).

Figure 5

Inhibition of carrageenan-induced paw edema in rats by ciclamilast. Ciclamilast (Cic) or indomethacin (Indo) was administered p.o. 30 min after intraplantar injection of carrageenan (100 μL of 1% carrageenan) into the left hind paw pad. At the specified times, paw volume was measured by a water-replacement plethysmometer. Statistical analysis was performed by one-way ANOVA (Dunnett's method) or Mann-Whitney t-test. ^* P < 0.05, ^** P < 0.01 and ^*** P < 0.001 versus vehicle group. Data represent the mean ± S.E.M. (n = 9-10/group).

Figure 6

Anti-inflammatory effect of ciclamilast on carrageenan-induced peritonitis in mice. Mice received vehicle or ciclamilast, p.o., followed by injection of 1 mg carrageenan diluted in 100 μL saline solution (i.p.) after 1 h. Mice were killed 4 h later, and the peritoneal cavity was washed with 1.5 mL of heparinized phosphate-buffered saline (PBS) to harvest the peritoneal cells. Statistical analysis was performed by one-way ANOVA (Dunnett's method) or Mann-Whitney t-test. ^* P < 0.05, ^** P < 0.01 and ^*** P < 0.001 versus vehicle group. Data represent the mean ± S.E.M. (n = 8/group).