Antiobesity action of e-polylysine, a potent inhibitor of pancreatic lipase

In vitro, e-polylysine (EPL) strongly inhibited the hydrolysis of trioleoylglycerol emulsified with phosphatidylcholine (PC) and taurocholate by either pancreatic lipase or carboxylester lipase. The EPL concentration required for 50% inhibition of pancreatic lipase, 0.12 mM, was eight times lower than the concentration of orlistat required for the same effect. The 50% inhibition concentration by EPL was affected by emulsifier species: it was increased z150 times, 70 times, and 230 times on gum arabic, phosphatidylserine, and phosphatidic acid emulsion, respectively, compared with PC emulsion. The 50% inhibition concentration by orlistat was little changed by emulsifier species. Gel-filtration experiments suggested that EPL did not bind strongly to pancreatic lipase, whereas orlistat did. To test the effect of EPL on obesity, mice were fed a high-fat diet containing 0.1, 0.2, or 0.4% EPL. EPL prevented the highfat diet-induced increase in body weight and weight of the liver and visceral adipose tissues (epididymal and retroperitoneal). EPL also decreased plasma triacylglycerol and plasma cholesterol concentrations and liver triacylglycerol content after they had been increased by the high-fat diet. The fecal weights of mice were increased by the high-fat diet containing EPL compared with the high-fat diet alone. Fecal lipid was also increased by the diet containing EPL. These data clearly show that EPL has an antiobesity function in mice fed a high-fat diet that acts by inhibiting intestinal absorption of dietary fat.—Tsujita, T., H. Takaichi, T. Takaku, S. Aoyama, and J. Hiraki. Antiobesity action of e-polylysine, a potent inhibitor of pancreatic lipase. J. Lipid Res. 2006. 47: 1852–1858. Supplementary key words orlistat . high-fat diet . obesity Pancreatic lipase is a key enzyme in dietary triacylglycerol absorption, hydrolyzing triacylglycerols to 2-monoacylglycerol and fatty acids. Typical substrates for this enzyme are long-chain triacylglycerols, which are separated from the aqueous medium by the surface phase. Thus, for catalysis to occur, lipase must be adsorbed on the substrate lipid surface (oil-water interface), and the nature of the surface of the substrate is an important factor for lipase activity. Enzymes are sometimes activated or denatured by surface adsorption. As a consequence of these properties, amphoteric substances would be expected to influence the surface properties of substrate lipid and might affect the lipase reaction rate. There have been many reports of lipase inhibitors derived from natural materials, for example, proteins (1, 2), phytic acid (3), and saponins (4). Most of these inhibitors are amphoteric substances. It is well known that bile salts and synthetic detergents behave as inhibitors of lipolysis (5, 6). Amphiphilic proteins, such as BSA and b-lactoglobulin (7), have been shown to inhibit lipase activity toward its triacylglycerol substrate. Basic materials also influence the lipase reaction rate. Basic carbohydrate, such as chitin-chitosan, inhibited the hydrolysis of trioleoylglycerol (TO) (8). Previously, we demonstrated that a basic protein, protamine and polylysine, strongly inhibited the hydrolysis of TO emulsified with phosphatidylcholine (PC) (9, 10). Polylysine has been suggested as a food antiseptic because it binds to some proteins, nucleic acids, viruses, or bacteria through electrostatic or hydrophobic interaction and inhibits their functions. Another form of polylysine, e-polylysine (EPL), is synthesized by linking the a-carboxyl groups of lysine with its e-amino groups. As a consequence of this linkage, it is not hydrolyzed by proteases, such as trypsin, but retains its basic character. Therefore, EPL is a candidate agent to inhibit intestinal lipid absorption while resisting proteolysis. Only a few substances interact directly with lipases themselves, one example being orlistat (tetrahydrolipstatin), a derivative of the naturally occurring lipase inhibitor orlistat produced from Streptomyces toxytricini, which strongly inhibits pancreatic lipase (11–13). The mechanism of lipase inhibition by orlistat is through a covalent bond to the active site serine of the lipase (14, 15). In this study, we compared the inhibition of lipase activity by EPL Manuscript received 12 April 2006 and in revised form 12 May 2006 and in re-revised form 16 May 2006 and in re-re-revised form 24 May 2006. Published, JLR Papers in Press, May 24, 2006. DOI 10.1194/jlr.M600168-JLR200 Abbreviations: EPL, e-polylysine; PA, phosphatidic acid; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PS, phosphatidylserine; TES, N-tris(hydroxylmethyl)-methyl-2-aminoethanesulfonic acid; TO, trioleoylglycerol. 1 To whom correspondence should be addressed. e-mail: [email protected] Copyright D 2006 by the American Society for Biochemistry and Molecular Biology, Inc. This article is available online at http://www.jlr.org 1852 Journal of Lipid Research Volume 47, 2006 by gest, on O cber 1, 2017 w w w .j.org D ow nladed fom and orlistat. We also examined the effect of EPL on obesity in mice induced by a high-fat diet. MATERIALS AND METHODS