Activation of PPARγ by rosiglitazone attenuates intestinal Cl⁻secretion

Abstract

The thiazolidinedione (TZD) drugs rosiglitazone (Ro) and pioglitazone (Po) are PPARgamma agonists in widespread clinical use as insulin-sensitizing agents in Type 2 diabetes. On the basis of recent evidence implicating PPARgamma as a positive modulator of intestinal epithelial differentiation, we hypothesized that TZD drugs might attenuate intestinal secretory function. To evaluate this possibility, we examined the effects of Ro and Po on electrogenic Cl- secretion [short-circuit current (I(sc))] in mouse intestinal segments and in cultured human intestinal epithelial cells (HT29-Cl.19A). As hypothesized, oral administration of Ro (20 mg.kg(-1).day(-1)) to mice for 8 days markedly reduced intestinal I(sc) responses to cAMP (forskolin)- and Ca2+ (carbachol)-dependent stimuli. In these Ro-treated mice, cholera toxin-induced intestinal fluid accumulation was reduced 65%. With continued Ro treatment, the I(sc) response to carbachol recovered significantly, whereas that to forskolin remained attenuated. Treatment of HT29 cells for 5 days with 10 muM Ro or Po in vitro brought about a similar hyposecretory state. In HT29 cells, the loss of cAMP-dependent Cl- secretion was attributable to a reduced expression of CFTR Cl- channel, KCNQ1 K+ channel, and Na-K-2Cl cotransporter-1 proteins. The transient loss of Ca2+-dependent Cl- secretion involved an impairment of basolateral Ca2+-stimulated K+ channel activity without a detectable loss of K(Ca)3.1 channel protein. Our results establish TZD drugs as important modulators of intestinal Cl- secretory function.

Stimulation of Murine Intestinal Secretion by Daily Genistein Injections: Gender-dependent Differences

“…Methods were similar to those described previously [18,[32][33]. As with these previously reported studies, we demonstrated a single band with the expected molecular weight of ~170 kD for CFTR.…”

“…Jejuna were later prepared for western blot analysis by homogenization. The western blot protocol was similar to that described previously [18]. Briefly, samples were analyzed for protein content, and ran on 4-12% Bis-Tris gels at 150 volts for ~ 1.5 hours.…”

Dietary Genistein Rescues Reduced Basal Chloride Secretion in Diabetic Jejunum via Sex-Dependent Mechanisms

“…Since, CFTR chloride channels provide the major route for chloride secretion into the jejunum lumen, we determined total CFTR protein present utilizing standard western blot techniques [18,[28][29][30]. We confirmed a single band with the expected molecular weight of ~170 kD for CFTR.…”

PPARγ Agonists, Modulation of Ion Transporters, and Fluid Retention

“…Oral administration of rosiglitazone to mice for 8 d reduces intestinal forskolinstimulated anion secretion and substantially inhibits choleratoxin-induced intestinal fluid accumulation. 15 In HT29 intestinal cells, 5 d of treatment with rosiglitazone inhibits cAMP-dependent Cl Ϫ secretion concomitantly with a decrease in the protein expression of CFTR, Na…”

“…15 Thus, the strongest and most consistent evidence to date suggests that the primary effect of PPAR␥ agonists in polarized epithelia is a decrease in the expression of Cl Ϫ channels. In summary, a compendium of data suggests that PPAR␥ agonists cause fluid retention through effects on the renal collecting duct.…”