triolein and retinol-palmitate

Essential fatty acid (EFA) deficiency induces fat malabsorption, but the pathophysiological mechanism is unknown. Bile salts (BS) and EFA-rich biliary phospholipids affect dietary fat solubilization and chylomicron formation, respectively. We investigated whether altered biliary BS and/or phospholipid secretion mediate EFA deficiency-induced fat malabsorption in mice. Free virus breed (FVB) mice received EFA-containing (EFA(+)) or EFA-deficient (EFA(-)) chow for 8 wk. Subsequently, fat absorption, bile flow, and bile composition were determined. Identical dietary experiments were performed in multidrug resistance gene-2-deficient [Mdr2((-/-))] mice, secreting phospholipid-free bile. After 8 wk, EFA(-)-fed wild-type [Mdr2((+/+))] and Mdr2((-/-)) mice were markedly EFA deficient [plasma triene (20:3n-9)-to-tetraene (20:4n-6) ratio >0.2]. Fat absorption decreased (70.1 +/- 4.2 vs. 99.1 +/- 0.3%, P < 0.001), but bile flow and biliary BS secretion increased in EFA(-) mice compared with EFA(+) controls (4.87 +/- 0.36 vs. 2.87 +/- 0.29 microl x min(-1) x 100 g body wt(-1), P < 0.001, and 252 +/- 30 vs. 145 +/- 20 nmol x min(-1) x 100 g body wt(-1), P < 0.001, respectively). BS composition was similar in EFA(+)- and EFA(-)-fed mice. Similar to EFA(-) Mdr2((+/+)) mice, EFA(-) Mdr2((-/-)) mice developed fat malabsorption associated with twofold increase in bile flow and BS secretion. Fat malabsorption in EFA(-) mice is not due to impaired biliary BS or phospholipid secretion. We hypothesize that EFA deficiency affects intracellular processing of dietary fat by enterocytes.

Topics: Animals; ATP Binding Cassette Transporter, Subfamily B; ATP-Binding Cassette Transporters; Bile; Bile Acids and Salts; Body Weight; Carbon Radioisotopes; Cholestanetriol 26-Monooxygenase; Cholesterol 7-alpha-Hydroxylase; Cytochrome P-450 Enzyme System; Dietary Fats; Diterpenes; Enterocytes; Fatty Acids; Fatty Acids, Essential; Homozygote; Kinetics; Liver; Malabsorption Syndromes; Mice; Mice, Knockout; Oleic Acid; Phospholipids; Polyethylene Glycols; Retinyl Esters; RNA, Messenger; Steroid Hydroxylases; Triolein; Tritium; Vitamin A

Various properties of retinyl ester hydrolysis in the liver and the retinal pigment epithelium (RPE) have been studied, yet the relationship between the retinyl ester hydrolase (REH) activities in these tissues of the same species is not known. In the present study, REH activities in bovine liver and RPE microsomes were compared to explore potential biochemical relationships of retinyl ester metabolism in these tissues. Rates of [3H]all-trans retinyl palmitate hydrolysis by liver and RPE were comparable (i.e., Vmaxapp approximately 300 pmol/min per mg; K(m)app approximately 30 microM), while hydrolysis of [3H]11-cis retinyl palmitate by RPE was significantly higher (Vmaxapp = 1,667 pmol/min per mg). When equimolar amounts (10 microM) of either [14C]triolein or unlabeled 11-cis retinyl palmitate were added to [3H]all-trans REH assays, all-trans REH activities in liver and RPE demonstrated similar time-dependent inhibition profiles. In contrast, hydrolysis of [3H]11-cis retinyl palmitate by RPE was relatively unaffected by addition of either [14C]triolein or unlabeled all-trans retinyl palmitate. Additionally, modification of the microsomal proteins with N-ethylmaleimide produced profound, dose-dependent alterations in K(m)app values for all-trans retinyl ester hydrolysis, whereas K(m)app for 11-cis REH in the RPE was not significantly altered. These results have elucidated common biochemical features of all-trans retinyl ester hydrolysis in liver and RPE. In contrast, hydrolysis of 11-cis retinyl ester in RPE is characterized by a distinctive substrate preference and unique biochemical properties.

Topics: Animals; Carboxylic Ester Hydrolases; Cattle; Diterpenes; Dose-Response Relationship, Drug; Ethylmaleimide; Isomerism; Microsomes, Liver; Pigment Epithelium of Eye; Retinyl Esters; Substrate Specificity; Triolein; Vitamin A

In previous studies, retinyl palmitate hydrolase activity in rat liver was partly characterized and was found to correlate and to partially copurify with hydrolytic activities against cholesteryl oleate and triolein. The present studies were designed to further explore relationships between these three lipid ester hydrolase activities, by use of non-hydrolyzable ether analogs of cholesteryl esters and acylglycerides. Cholesteryl ether analogs were potent inhibitors of all three hydrolase activities with relative potencies for the series of ethers of: linoleyl greater than oleyl = palmitoyl greater than n-butyl = n-propyl greater than ethyl = methyl. Retinyl palmitate hydrolase activity was most strongly inactivated by this series of analogs, with 48-86% of the activity inhibited at cholesteryl ether levels of 1 microM. The acylglyceride ether analogs were much weaker inhibitors of the three hydrolase activities, with the triolein, diolein and dipalmitin analogs showing similar inhibitory potencies, greater than that of the monolein and monopalmitin analogs. The data demonstrate the potential usefulness of ether analogs of cholesteryl esters and acylglycerides for exploring some of the characteristics of lipid ester hydrolase activities.

Topics: Animals; Carboxylic Ester Hydrolases; Cholesterol; Cholesterol Esters; Diterpenes; Ethers; Glycerol; Lipase; Liver; Rats; Rats, Inbred Strains; Retinyl Esters; Sterol Esterase; Triolein; Vitamin A