Angiotensin II Inhibits P‐glycoprotein in Human Intestinal Epithelial cells

Abstract

P‐glycoprotein (P‐gp/MDR1) plays an important role in the maintenance of intestinal homeostasis. Dysregulation of Pgp function and expression have been implicated in the pathogenesis of IBD and MDR1 null mice spontaneously develop severe colitis. However, the inhibitory mechanisms of Pgp function in inflammation are not fully understood. Angiotensin II (Ang II) has been shown to exert pro‐inflammatory effects in the gut. It is increased in patients with Crohn's disease & animals with experimental colitis. Whether, Ang II directly influences Pgp is not known. Therefore, we investigated the modulation of Pgp function and expression by Ang II in human intestinal Caco2 cells. Ang II (10 nM, 60 min) inhibited Pgp activity as measured by verapamil‐sensitive 3H‐Digoxin flux (~60 %, P<0.05) with no effect at 1 nM. Also, the inhibitory effects of Ang II were observed at 60 min but not at 15 & 30 min time points. Ang II‐mediated effects on Pgp function were receptor‐mediated as the ATR1 inhibitor, losartan blocked Pgp inhibition by Ang II. Specific inhibitors of PI3 kinase, LY294002 or Akt, triciribine attenuated the effects of Ang II on Pgp activity suggesting the involvement of PI3 kinase & Akt mediated pathways. Ang II also induced Akt phosphorylation in Caco2 cells. Cell surface biotinylation studies showed that Ang II‐mediated inhibition of Pgp activity was associated with a decrease in its surface membrane expression. In conclusion, current studies demonstrate that Ang II inhibits Pgp function & membrane expression and provide novel insights into the mechanisms underlying the pro‐inflammatory role of Ang II in intestinal inflammation (Supported by NIDDK and Dept of Veteran Affairs)