| 1. |
- Chen, Qi, et al.
(author)
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Digestion of triacylgycerols containing longchain polyenoic fatty acids in vitro by colipase dependent lipase and human milk bile salt stimulated lipase
- 1994
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In: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002. ; 121:2, s. 239-243
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Journal article (peer-reviewed)abstract
- To assess the role of human milk bile salt-stimulated lipase (BSSL) in the digestion of polyunsaturated ester bonds of triacylglycerols, hydrolysis of docosahexaenoic acid (22:6(n − 3)) ester bonds was compared to that of oleic acid (18:1(n − 9)) or arachidonic acid (20:4(n − 6)) esters. As model substrates, we used rat chylomicrons obtained after feeding human milk fat globules and radiolabeled fatty acids. Radiolabeled chylomicrons were incubated with colipase-dependent pancreatic lipase, with BSSL, or with both enzymes in combination. Both enzymes hydrolyzed 18:1 more efficiently than 22:6 esters. With colipase-dependent lipase there was a large accumulation of 22:6 in diacylglycerol whereas with BSSL it accumulated mainly in monoacylglycerol. Esters containing 20:4 were hydrolyzed by BSSL as efficiently as 18:1 but this fatty acid also accumulated as diacylglycerol with colipase-dependent lipase. At low bile salt concentrations, as found in duodenal contents of newborns, colipase-dependent lipase was virtually unable to hydrolyze esters of 20:4 and 22:6 whereas BSSL hydrolyzed these esters at appreciable rates. Combining the two enzymes gave the most efficient hydrolysis of all fatty acids tested regardless of bile salt concentrations. BSSL may thus have a physiological role in completing duodenal hydrolysis of milk triacylglycerols containing 22:6- or 20:4-esters to free fatty acids and monoacylglycerol.
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| 2. |
- Chen, Qi, et al.
(author)
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Lipoprotein receptor mediated metabolism of 14C arachidonic acid labelled chylomicron remnants by Hep G2 cells
- 1992
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In: Lipids. - 0024-4201. ; 27:9, s. 664-668
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Journal article (peer-reviewed)abstract
- During lipolysis of chylomicron triacylglycerol by lipoprotein lipase, arachidonic acid (AA) esters are hydrolyzed at a slower rate than the predominant 16-18 carbon fatty acid esters. The further metabolism of the AA that is hereby enriched in the chylomicron remnant acylglycerols has not been investigated. In the present study, we examined the low density lipoprotein (LDL) dependent and independent metabolism of [14C]AA present in chylomicron remnants in the human hepatoma cell line Hep G2. Mesenteric duct cannulated rats were fed [14C]AA and [3H]cholesterol in corn oil, and the chyle obtained was injected intravenously into hepatectomized rats to form chylomicron remnants labeled with [14C]AA in the triacylglycerol (TG) and with 3H in the cholesteryl ester portion. The remnants were then incubated with Hep G2 cells. The uptake of [14C]AA within 2-4 h was similar to that of [3H]cholesteryl ester. After uptake into the cells, [14C]AA was preferentially incorporated into phospholipids, a high proportion being found in phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol. [14C]AA and [3H]cholesteryl ester uptake were influenced to similar extents by factors unknown to regulate the LDL receptor and by an anti-LDL receptor antibody. Addition of compactin thus increased the uptake of [14C]AA by 50% in 4 h and mevalonolactone decreased the uptake by 86%. Using an anti-LDL receptor antibody, 25.0% of [3H]cholesterol/cholesteryl ester and 37.7% of [14C]AA binding to the cells at 4 degrees C were blocked. There was no lipolysis of [14C]TG or [14C]diacylglycerol by lipase secreted into the medium during incubations.
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| 3. |
- Hernell, Olle, et al.
(author)
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Does the bile salt stimulated lipase of human milk have a role in the use of the milk long-chain polyunsaturated fatty acids?
- 1993
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In: Journal of Pediatric Gastroenterology and Nutrition - Jpgn. - 1536-4801 .- 0277-2116. ; 16:4, s. 426-431
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Journal article (peer-reviewed)abstract
- Long-chain polyunsaturated (LCP) fatty acids derived from linoleic (18:2 n-6) and alpha-linolenic (18:3 n-3) acids are considered essential nutrients in preterm infants. The efficiency by which such fatty acids are released as absorbable products from triacylglycerol was explored in vitro using rat chylomicron triacylglycerol as substrate. When incubated with purified human pancreatic colipase-dependent lipase and colipase, arachidonic acid (20:4 n-6) was released less efficiently than linoleic acid from such triacylglycerol. This difference was not seen when purified human milk bile salt-stimulated lipase (BSSL) was incubated with the triacylglycerol substrate, and it was almost abolished when colipase-dependent lipase (with colipase) and BSSL acted simultaneously, as they do in breast-fed infants. There was no difference in arachidonic acid and eicosapentaenoic acid (20:5 n-3) release rates with either colipase-dependent lipase or BSSL, albeit the release was more rapid with the milk enzyme than with colipase-dependent lipase. Again, the most efficient release as absorbable free fatty acids was achieved when the two lipases operated together. The relative resistance to hydrolysis of arachidonic acid and eicosapentaenoic acid by colipase-dependent lipase was best explained by the localization of the first double bond to the delta-5 position of the respective fatty acid. The results obtained suggest that BSSL is of importance for the efficient use of human milk LCP fatty acids.
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