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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.

The rates of activation of procolipase, prophospholipase (proPLA2), chymotrypsinogen, and trypsinogen were studied after incubation of human pancreatic juice with porcine enterokinase in vitro. Under the conditions chosen procolipase was fully activated within 10 min of incubation. Full activation of phospholipase (PLA2) was seen within 15 min, whereas complete activation of chymotrypsin and trypsin was not seen until after 30 to 60 min, respectively. The different proenzymes probably differ in their suitability as substrates for trypsin. A physiologic consequence of a differentiated activation of the pancreatic proenzymes in vivo could be a delayed proteolytic degradation of the lipolytic enzymes in the intestine.

The existence of a specific lysophospholipase in human pancreatic juice was evaluated. The proteins were separated by a series of chromatographic steps including Sephacryl S-200, cholate-Sepharose 4B, Sephadex G-100 and CM-Sephadex G-50. The enzyme activities against 1-palmitoyl lysolecithin (LL) as well as tributyrin (TB) and p-nitrophenyl butyrate (PNPB) were determined in all the fractions of these purification procedures. Enzyme activity against LL was always eluted in parallel with activities against TB and PNPB, and no unique activity against LL could be found. The specific activity against LL was 40-times lower than that against PNPB and 200-times lower than that against TB. It is concluded that there is no unique lysophospholipase in human pancreatic juice and that the hydrolysis of lysolecithin is most likely performed by carboxyl ester lipase.

Purified antibodies to human colipase86 were coupled to CNBr-activated Sepharose 4B. The immunoadsorption column thus obtained was used to purify procolipase from human pancreatic juice in one step by immunoaffinity chromatography. A single form of procolipase was obtained, having similar biological properties as previously characterized procolipases from horse and pig. The sequence of the N-terminal propeptide was determined to be Ala-Pro-Gly-Pro-Arg. In bovine, equine and porcine procolipases the corresponding N-terminal sequence is Val-Pro-Asp-Pro-Arg.