Evidence for specific ceramidase present in the intestinal contents of rats and humans

A neutral ceramidase activity stimulated by bile salt was previously identi fied in the intestinal content. Recently, bile salt stimulated lipase (BSSL ) was found to have ceramidase activity. It is unknown whether the ceramida se activity previously found is attributable to BSSL. To address this quest ion, we compared the behaviors of high quaternary aminoethyl (HQ) anion exc hange chromatography, the distributions, the stability, and the responses t o lipase inhibitor between ceramidase and pancreatic BSSL. The proteins fro m whole small intestinal contents of humans and rats were precipitated by a cetone and dissolved in 20 mM Tris buffer pH 8.2. These proteins had neutra l ceramidase activity but not BSSL activity against p-nitrophenyl acetate. When the proteins were subject to HQ chromatography, two peaks of ceramidas e activity were identified, which had acid and neutral pH optima, respectiv ely. Neither of them had BSSL activity against p-nitrophenyl acetate. Weste rn blot using BSSL antiserum failed to identify BSSL protein in the fractio ns with high neutral ceramidase activity. In rat intestinal tract, pancreat ic BSSL activity was high in the duodenum and declined rapidly in the small intestine, whereas neutral ceramidase activity was low in the duodenum and maintained a high level until the distal part of the small intestine. In a ddition, orlistat, the inhibitor of lipase, abolished human BSSL activity a gainst p-nitrophenyl acetate and slightly reduced its activity against cera mide but had no inhibitory effect on ceramidase activity isolated by HQ chr omatography. In conclusion, we provide the evidence for a specific ceramida se other than pancreatic BSSL present in the intestinal content. The enzyme may play important roles in digestion of dietary sphingolipids.