Lingual lipase in cystic fibrosis. Quantitation of enzyme activity in the upper small intestine of patients with exocrine pancreatic insufficiency.

We have measured the level of lingual lipase activity in gastric and duodenal aspirates of five patients with cystic fibrosis (CF) and pancreatic insufficiency. Lingual lipase activity (measured in vitro by the hydrolysis of long-chain triglyceride, tri-[3H]olein, at pH 4.2 and expressed in nanomoles FFA released per milliliter aspirate per minute) and pH in gastric and duodenal aspirates were measured at 10-min intervals during a a 30-min basal period and at 15-min intervals during a 2-h period after the ingestion of a test meal. In gastric aspirates, lingual lipase activity decreased from basal levels of 200 +/- 34 nmol FFA released per milliliter per minute (similar to values reported previously in normal subjects (Hamosh M., H. L. Klaeveman, R. O. Wolf, and R. O. Scow, 1975, J. Clin. Invest., 55:908-913) to 79 +/- 15 nmol FFA/ml per min during the first postprandial hour and returned to basal levels during the second postprandial hour, (206 +/- 39 nmol FFA/ml per min). Duodenal aspirates, obtained during basal conditions, had lingual lipase activity similar to that in the stomach, 178 +/- 63 nmol FFA/ml per min. Enzyme activity levels were 56 +/- 14 and 113 +/- 29 during the first and second postprandial hours. Measurements of total lipase activity delivered to the ligament of Treitz showed that lingual lipase amounted to 91.22 +/- 4.06% of the total lipase activity in the upper small intestine during the 150-min study period. The basal and postprandial gastric pH levels in the five CF patients studied (3.2 +/- 0.44, 4.0 +/- 0.16, and 4.4 +/- 0.4 for basal and first and second postprandial hours, respectively) did not differ from previously reported values for normal subjects. The pH of duodenal aspirates was however significantly lower (P less than 0.001) in CF patients, both under basal conditions (5.0 +/- 0.26) and during the first and second postprandial hours (4.9 +/- 0.13 and 4.4 +/- 0.36, respectively), than in normal subjects. The low postprandial duodenal pH enables lingual lipase to act not only in the stomach but to continue the hydrolysis of dietary fat in the upper small intestine of CF patients. The data presented show that lingual lipase remains fully active in CF and accounts for greater than 90% of total lipase activity in the upper small intestine. We suggest that, because of low intestinal pH in CF, enzyme replacement therapy containing lingual lipase could improve fat absorption in CF patients to a greater extent than the pancreatic preparations now in use.