Alkaline sphingomyelinases and ceramidases of the gastrointestinal tract

In addition to the acid and neutral sphingomyelinases (SMase) that occur in most tissues, distinct alkaline sphingomyelinases occur in the mucosa of t he gastrointestinal tract and human bile. These enzymes exhibit characteris tic properties with regard to bile-salt dependence, protease resistance, an d longitudinal distribution in the gut. Alkaline SMase has now been partial ly purified from human bile and from rat small intestine. It is thought to have a role in sphingomyelin (SM) digestion but may also be important for t he generation of antiproliferative sphingolipid messengers in the gut. It o ccurs throughout the whole length of the intestine and also in the colon. I t is decreased in colon cancer tissue compared to surrounding mucosa and is extremely low in colon mucosa from patients with familial adenomatous poly posis (FAP). This chapter reviews the properties and potential physiologica l and pathophysiological significance of alkaline SMase. It also briefly su mmarizes the knowledge about sphingolipid digestion and about the ceramidas es of the gut. (C) 1999 Published by Elsevier Science Ireland Ltd. All righ ts reserved.