INHIBITION OF PANCREATIC ELASTASE BY SULFATED LIPIDS IN THE INTESTINAL-MUCOSA

Sulfated lipids, cholesterol sulfate (CS) and (ISO3)-S-3-GalCer, are c ommonly present in the epithelia of the digestive tracts of pigs, huma ns, rabbits, and rats. CS was the only sulfated lipid in the esophagea l epithelia of these mammals, and (ISO3)-S-3-GalCer, together with CS, was detected in the epithelia of the gastrointestinal tracts, at a co ncentration higher than 0.05 mu mol per gram of dry weight. Although n o sulfated lipids were present in the pancreatic duct, they were found in relatively high concentrations in the duodenal, jejunal, and ileal epithelia. To elucidate the functional significance of sulfated lipid s in the digestive tract, we determined the effect of CS and (ISO3)-S- 3-GalCer on the activities of pancreatic and Pseudomonas aeruginosa el astases and found that both characteristically inhibited the pancreati c elastase but not the P. aeruginosa elastase. Desulfation of CS and ( ISO3)-S-3-GalCer abolished their inhibitory activity, and other membra ne constituents including free fatty acids, phospholipids, and ganglio sides failed to inhibit pancreatic elastase. In addition, steroid sulf ates, such as dehydroepiandrosterone sulfate and pregnenolone sulfate, did not exhibit any inhibitory activity toward pancreatic elastase, i ndicating that the sulfate group and a suitable hydrophobic side chain are required in the inhibition of elastase. Inhibition of elastase by sulfated lipids occurred in a dose-dependent manner, and the molar ra tios of CS and (ISO3)-S-3-GalCer to elastase at which the enzyme activ ity was inhibited to 50% of the maximum level were 6:1 and 9:1, respec tively. CS-treated elastase had the same K-m and a lower V-max compare d with the untreated enzyme, and sulfated lipids were observed to bind tightly to the enzyme, suggesting irreversible inhibition. Thus, CS a nd (ISO3)-S-3-GalCer in the digestive tracts of mammals were shown to function as epithelial inhibitors of pancreatic elastase.