Summary Blastocystis is an enteric parasite that causes acute and chronic intestinal infections, often non-responsive to conventional antibiotics. The effects of Blastocystis infections on human epithelial permeability are not known, and molecular mechanisms of Blastocystis-induced intestinal pathology remain unclear. This study was conducted to determine whether Blastocystis species alters human intestinal epithelial permeability, to assess whether these abnormalities are rho kinase (ROCK)-dependent, and to investigate the therapeutic potential of the HMG-CoA reductase inhibitor Simvastatin in altered intestinal epithelial barrier function. The effect of metronidazole resistant (Mzr) Blastocystis isolated from a symptomatic patient on human colonic epithelial monolayers (Caco-2) was assessed. Modulation of enterocyte myosin light chain phosphorylation, transepithelial fluorescein isothiocyanate-dextran fluxes, transepithelial resistance, cytoskeletal F-actin and tight junctional zonula occludens-1 (ZO-1) by parasite cysteine proteases were measured in the presence or absence of HMG-CoA reductase and ROCK inhibition. Blastocystis significantly decreased transepithelial resistance, increased epithelial permeability, phosphorylated myosin light chain and reorganized epithelial actin cytoskeleton andZO-1. Thesealterations were abolished byinhibition of enterocyte ROCK, HMG-CoA reductase and parasite cysteine protease. Our findings suggest that cysteine proteases of Mzr Blastocystis induce ROCK-dependent disruption of intestinal epithelial barrier function and correlates with reorganization of cytoskeletal F-actin and tight junctional ZO-1. Simvastatin prevented parasite-induced barriercompromise, suggesting a therapeutic potential of statins in intestinal infections.
