Degree of in vivo inhibition of human gastric and pancreatic lipases by Orlistat (Tetrahydrolipstatin, THL) in the stomach and small intestine.

Background and Aims: Orlistat, a lipase inhibitor, strongly inhibits the activities of all gastric/pancreatic lipases except pancreatic phospholipase A(2)in vitro. In clinical use, for obesity treatment, it induces a variable degree of weight loss and steatorrhoéa. The aim of this study was to examine the degree of in vivo inhibition of individual gastric/pancreatic lipases by Orlistat in man, when given as a capsule or mixed into a test meal in the form of an optimal substrate for the lipases.
Methods: Twelve male volunteers were intubated twice with a triple lumen nasal-gastric-duodenal tube and were given a balanced test meal with or without 60 mg Orlistat. Three conditions were compared: (a) Orlistat given as a capsule with the meal, (b) Orlistat mixed into the test meal before ingestion, and (c) test meal without Orlistat. Samples were collected at six 30 min intervals, from stomach, mid-duodenum, and ligament of TreitY. Activities and immune-reactive masses of gastric lipase, pancreatic lipase, carboxyl ester lipase, colipase, and mass of non-polar lipid classes were determined.
Results: In vivo effects on the enzyme activities were more pronounced when Orlistat was mixed with the meal than when given as a capsule (7%, 10%, 1% vs 49%, 54%, 34% of normal activity), respectively. Despite efficient inhibition of the lipases, an extensive hydrolysis of the emulsified lipids of the test meal occurred. Orlistat did not affect the immune-reactive amounts of lipases.
Conclusions: Orlistat causes a pronounced in vivo inhibition of gastric and pancreatic lipases in humans. The mixing with the substrate and the fact that little residual lipase activity is necessary to hydrolyse optimally emulsified lipids are likely to be limiting factors for the effect of the drug in clinical practice.