Activation of PPARγ by rosiglitazone attenuates intestinal Cl − secretion

The thiazolidinedione (TZD) drugs rosiglitazone (Ro) and pioglitazone (Po) are PPARγ agonists in widespread clinical use as insulin-sensitizing agents in Type 2 diabetes. On the basis of recent evidence implicating PPARγ 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 Ca 2+ (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 μM 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 Ca 2+ -dependent Cl − secretion involved an impairment of basolateral Ca 2+ -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.