Dextran sulfate sodium-induced colonic histopathology, but not altered epithelial ion transport, is reduced by inhibition of phosphodiesterase activity

Abstract

Inhibition of phosphodiesterase (PDE) activity is beneficial in models of arthritis and airway inflammation. Here we assessed the ability of PDE inhibitors to modulate colitis by exposing mice to 4% (w/v) dextran sulfate sodium (DSS) drinking water for 5 days with or without rolipram, an inhibitor of PDE type 4, or the nonselective PDE inhibitor, pentoxifylline (both at 5 mg/kg, i.p., twice daily). Controls received saline, vehicle, or drug only. Colonic histology, myeloperoxidase (MPO) and tumor necrosis factor-alpha (TNF-alpha) levels, and epithelial ion transport (baseline and stimulated by electrical nerve stimulation, carbachol, and forskolin) were examined. DSS-treated mice displayed a variable diarrhea, significant histopathology in the mid-distal colon, elevated MPO activity, and reduced (>50%) responses to all three pro-secretory stimuli. Treatment with rolipram, and to a lesser extent pentoxifylline, significantly reduced the severity of the colonic histopathology and MPO levels. Neither PDE inhibitor had any affect on the diminished ion transport events caused by DSS-induced colitis. However, although stimulated ion transport events were still reduced 3 days after DSS treatment, colonic segments from DSS + rolipram-treated mice displayed enhanced recovery in their secretory responsiveness, particularly to carbachol. These findings indicate that specific PDE4 inhibition can significantly reduce the tissue damage that accompanies colitis and enhance recovery of normal colonic function.

Figure 1.

Bar chart showing average daily DSS water intake as a percentage of normal water intake in time-matched control mice. DSS, 4% (w/v) for 5 days; ROL, given i.p. at 5 mg/kg (ie, 100 μg/mouse) once or twice daily (twice daily); PTX, given i.p. at 5 mg/kg (ie, 100 μg/mouse) twice daily. Mean values of 3 to 5 separate experiments with 3 to 4 mice per group in each experiment; means ± SEM; *, P < 0.05 compared to control.

Figure 2.

Representative photomicrographs of colonic segments from mice given regular water, ie, control (a); ROL only, twice daily (b); DSS only (c); DSS + ROL, twice daily (d); DSS + PTX, twice daily (e); and mice treated with DSS + ROL, twice daily for 5 days and then allowed to recover for an additional 3 days (f). m, muscle; small arrowheads denote edema; large arrowheads and arrows indicate inflammatory infiltrate. See Figure 1 ▶ legend for abbreviations and treatment regimen.

Figure 3.

Bar chart showing colonic damage score after exposure to DSS ± PDE inhibitors. Means ± SEM; n = 9 to 15, except DSS + ROL (x1) where n = 4. *,#, δ, statistically different (P < 0.05) groups compared to each other and control (CON). See Figure 1 ▶ legend for abbreviations and treatment regimen.

Figure 4.

Bar charts showing the change in short-circuit current (ΔIsc) in colonic segments in response to electrical nerve stimulation (A), carbachol (10⁻⁴ mol/L) (B), and forskolin (10⁻⁵ mol/L) (C) after 5 days of DSS exposure ± PDE inhibitors. Means ± SEM; n = 9 to 15; *, P < 0.05 compared to controls (CON). See Figure 1 ▶ legend for treatments.

Figure 5.

Bar chart showing viability of murine epithelial (IEC.4.1) cells exposed to 1% or 2% DSS for 24 hours in vitro ± ROL (10⁻ mol/L, single addition) as determined by trypan blue dye exclusion, where increased positivity indicates increased cell death. Data are means ± SEM and are presented as percentage of controls cells cultured in media only; n = 3 experiments, with three replicates/condition in each experiment. *, P < 0.05 compared to controls; positive control of distilled water resulted in 100% positivity (data not shown).