Intestinal Lipase

FIGURE 24.3 (a) A duct at the junction of the pancreas and duodenum secretes pancreatic juice into the duodenum, the first portion of the small intestine, (b) Hydrolysis of triacylglycerols by pancreatic and intestinal lipases. Pancreatic lipases cleave fatty acids at the C-1 and C-3 positions. Resulting monoacylglycerols with fatty acids at C-2 are hydrolyzed by intestinal lipases. Fatty acids and monoacylglycerols are absorbed through the intestinal wall and assembled into lipoprotein aggregates termed chylomicrons (discussed in Chapter 25). 

The fatty acids of triacylglycerols furnish a large fraction of the oxidative energy in animals. Dietary triacylglycerols are emulsified in the small intestine by bile salts, hydrolyzed by intestinal lipases, absorbed by intestinal epithelial cells, reconverted into triacylglycerols, then formed into chylomicrons by combination with specific apolipoproteins. 

Many carbohydrate-based fat substitutes are mixtures of sucrose esters formed by chemical transesterification or interesterification of sucrose with one to eight FAs. The class with six to eight FAs are called sucrose FA polyesters. These molecules are too large to be broken down by intestinal lipase enzymes and, for that reason, do not show any caloric value (Voragen, 1998). 

CASTOR OIL, Ricini oleum This is the fixed oil pressed from the ripe seeds of Rici-nus communis L., family Euphorbiaceae. This oil contains 75-80% of triglycerides of the fatty acid ricinoleic acid (12-hydro-9,10-cis-octadecenoic acid). Intestinal lipases can release this acid which has local stimulating effects on motility similar to that of the anthranoids. 

After triacylglycerols are emulsified (solubilized) by mixing with bile salts, they are digested by intestinal lipases, the most important of which is pancreatic lipase. The products, fatty acids and monoacylglycerol, are transported into enterocytes and resynthesized to form triacylglycerol. The triacylglycerol molecules, along with newly synthesized phospholipid and protein, are then incorporated into chylomicrons. After the chylomicrons are transported into lymph, via exocytosis, and then blood, they are taken up by peripheral tissues. 

Lipoprotein lipase and hepatic lipase are two lipases that degrade triacylglycerols in lipoproteins (Chapter 19) and also demonstrate significant PL A, activity. The enzymes have 50% sequence identity and are members of a superfamily of lipases and phospholipases that share the G-X-S-X-G motif at the active site and an Asp-His-Ser triad that is required for catalysis. Hepatic lipase is about 2-3-fold more efficient at hydrolyzing phospholipids than is lipoprotein lipase and has lysophospholipase activity. Another lipase, intestinal lipase, has lysophospholipase activity and is also referred to as a PLB. 

An alternative possible mechanism of hypolipidemic and hypocholesterolemic action of chitosan could be the inhibition of intestinal lipases. A limited work on inhibition of pancreatic lipase by neomycin in humans (31) and in vitro (32). and by cellulose and xylan (32) also in vitro have been reported. No work on the possible inhibition of intestinal lipases by chitosan has been published yet. 

Therefore, the possibility of encapsulating probiotics with lipid matrices is an interesting proposal, once lipids are digested by intestinal lipases, enabling the release of the microorganisms in the site where they are supposed to act, which is essential ensure their health benefits (Nori et al., 2009 Favaro-Trindade et al., 2011 Pedroso et al. 2012, 2013 Okuro et al. 2013b), as shown in Figure 5.2. 

Castor oil contains a triglyceride of ricinoleic acid which is hydrolyzed by intestinal lipases to glycerol and ricinoleic acid, which has cathartic effects. Allergic reactions such as angioedema, rhinitis, asthma, and scarlatiniform rashes have been described but seem to be rare reactions to this common laxative (Bennett and Schwartz 1934 Blank 1945). 

Salts of B.a. reduce surface tension and emulsify fats, so that they can be enzymatically degraded and absorbed in the intestine. Lipases are also activated by B.a. Humans produce 20 30g B.a. per day, and 90 % of this is resorbed in the intestine and returned to the liver in the enterohepatic drculation. One liter bile contains about 30 g B.a. 

Intestinal lipase - Monoglyceiides Glycerol, fatty aads. 

The transport of lipids into the intestinal epithelial ceUs requires their solubilization in bite acid micelles. First, the solubilization facilitates the hydrolysis of fatty acid ester bonds by the intestinal lipases. Second, the transport into the enterocytes requires the formation of a properly structured bile acid micelle. 

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