AIM To elucidate the role of proton pump inhibitors(PPIs) in collagenous disease, direct effect of PPI on colonocytes was examined.METHODS Collagenous colitis is a common cause of non-bloody, watery diarrhea. Recently, there has been increasing focus on the use of proton PPIs as a risk factor for developing collagenous colitis. Mouse CT26 colonic cells were treated with PPI and/or PPI-induced alkaline media. Expression of fibrosis-associated genes was examined by RT-PCR. In human materials, collagen expression was examined by immunohistochemistry.RESULTS CT26 cells expressed a Na+-H+ exchanger gene(solute carrier family 9, member A2). Treatment with PPI and/or PPI-induced alkaline media caused growth inhibition and oxidative stress in CT26 cells. The treatment increased expression of fibrosis inducing factors, transforming growth factor β and fibroblast growth factor 2. The treatment also decreased expression of a negative regulator of collagen production, replication factor C1, resulting in increased expression of collagen types Ⅲ and Ⅳ in association with lipid peroxide. In biopsy specimens from patients with collagenous colitis, type Ⅲ and Ⅳ collagen were increased. Increase of type Ⅲ collagen was more pronounced in PPI-associated collagenous colitis than in non-PPI-associated disease. CONCLUSION From these findings, the reaction of colonocytes to PPI might participate in pathogenesis of collagenous colitis. AIM To elucidate the role of proton pump inhibitors (PPIs) in collagenous disease, direct effect of PPI on colonocytes was examined. METHODS Collagenous colitis is a common cause of non-bloody, watery diarrhea. Recently, there has been increasing focus on the use of proton PPIs as a risk factor for developing collagenous colitis. Mouse CT26 colonic cells were treated with PPI and / or PPI-induced alkaline media. Expression of fibrosis-associated genes was examined by RT-PCR. by immunohistochemistry. RESULTS CT26 cells expressed a Na + -H + exchanger gene (solute carrier family 9, member A2). Treatment with PPI and / or PPI-induced alkaline media caused growth inhibition and oxidative stress in CT26 cells. The treatment increased expression of fibrosis inducing factors, transforming growth factor β and fibroblast growth factor 2. The treatment also decreased expression of a negative regulator of collagen production, replication factor C1, resul In biopsy specimens from patients with collagenous colitis, type Ⅲ and Ⅳ collagen were increased. Increase of type Ⅲ collagen was more pronounced in PPI-associated collagenous colitis than in non -PPI-associated disease. CONCLUSION From these findings, the reaction of colonocytes to PPI did participate in pathogenesis of collagenous colitis.