Fat Digestion by Lingual Lipase: Mechanism of Lipolysis in the Stomach and Upper Small Intestine

Abstract

Summarylipid in an acid environment (pH 3.0-6.0), could continue to actTen to 30% of dietary fat is hydrolyzed in the stomach by lingual lipase, an enzyme secreted from lingual serous glands. We investigated the substrate specificity of this enzyme as well as the potential of lingual lipase to act in the upper small intestine i.e., in the presence of bile salts and lecithin. The data presented show that partially purified preparations of rat lingual lipase and the lipase in gastric aspirates of newborn infants have identical substrate specificity: medium-chain triglycerides were hydrolyzed at rates 5-%fold higher than long-chain triglycerides; the rat and human enzymes do not hydrolyze the ester bond of lecithin or cholesteryl-ester. In contrast to pancreatic lipase, the hydrolysis of triglycerides by lingual lipase is not inhibited by lecithin. But, similar to pancreatic lipase the activity of lingual lipase is inhibited by bile salts, the extent of inhibition varying with its nature and concentration. This inactivation is not prevented by colipase but is partially averted by lipids and protein, suggesting that lingual lipase can remain active in the duodenum. The pH optimum of the enzyme (2.2-6.5 in the rat and 3.5-6.0 in human gastric aspirates) is compatible with continued activity in the .upper small intestine, especially during the neonatal period, when the luminal pH is under 6.5. The marked variation in lipase activity levels in gastric aspirates of newborn infants is probably due to individual variations in enzyme amounts. The characteristics of the lipase are however identical in infants with low, intermediate or high activity levels. Our results indicate that hydrolysis of dietary fat by lingual lipase may not be limited to the stomach but may continue in the upper small intestine. Abbreviations CMC, critical micellar concentration FFA, free fatty acid Up to one-third of dietary fat is hydrolyzed in the stomach by lingual lipase (2 1,27,28) an enzyme secreted from lingual serous glands (23,27). Fat digestion in the stomach produces mainly partial glycerides and FFA, amphiphilic substances that help disperse the fat in the stomach and intestine (56). The gastric digestion of fat greatly enhances further hydrolysis of fat by pancreatic lipase in the small intestine (6,45). Initial lipolysis in the stomach, a necessary step for normal fat absorption (45, 5 l), becomes a much more important process in conditions of physiologic or pathologic pancreatic insufficiency, such as prematurity (22,37,6 1,63) or cystic fibrosis (I 3, 39). Recent studies show that the duodenal pH is significantly lower than normal in pancreatic insufficiency (14, 15) because of impaired bicarbonate secretion (20). In these cases lingual lipase, which hydrolyzes in the upper small intestine (1 3).This study investigated the activity of lingual lipase under the conditions prevailing in the stomach and upper small intestine. The questions that we asked were the following: Does lingual lipase hydrolyze other dietary lipids such as leci...

Antiviral and antibacterial lipids in human milk and infant formula feeds.

“…Some contained a supplement of cows' milk protein (60:40 blend of whey proteins and caseins), calcium, phosphorus, and sodium. '4 The protein content (16)(17)(18)(19)(20)(21)(22) Stomach aspirates obtained from five infants three hours after they have been fed were also tested for antimicrobial activity. The antiviral activities of four of these five aspirates were comparable at one and three hours; the remaining three hour aspirate had no antiviral activity.…”

Lipase and Pepsin Activities in the Stomach Mucosa of the Suckling Dog

“…The emulsion consisted of labeled tri['H]olein, carrier triolein (200 pmol), and phosphatidylcholine (15 pmol) in 3.3 ml anhydrous glycerol. The emulsion was prepared on ice as previously described [26] using a Polytron PCU-2-110 sonifier (Brinkman Instru ments, Westbury, N.Y.). The emulsion was stored at room temperature and remained stable for several weeks.…”

Interactions of the Salivary and Gastrointestinal Systems

“…Lingual lipase (LL) is produced by Ebner's glands, serous salivary glands in the posterior one-third of the tongue [51], LL hydrolyzes triglycerides to form protonated fatty acids and diglycerides [52], Milk fat globules are readily hydrolyzed by LL [53]. The optimal pH for lipolysis by human LL is 3.5-6.0, and it is stable over a pH range of 1.6-8 [52,54], It is accepted that LL is active in the stomach. However, the relative contribu tions of lingual and gastric lipase to pre-duodenal lipolysis in normal persons is poorly understood [54], Several workers have sug gested that LL may be active in the small intestine as well [52.…”