trilinolein and tripalmitin

Lung surfactant mainly comprises phosphatidylcholines (PC), together with phosphatidylglycerols and surfactant proteins SP-A to SP-D. Dipalmitoyl-PC (PC16:0/16:0), palmitoylmyristoyl-PC (PC16:0/14:0), and palmitoylpalmitoleoyl-PC (PC16:0/16:1) together comprise 75-80% of surfactant PC. During alveolarization, which occurs postnatally in the rat, PC16:0/14:0 reversibly increases at the expense of PC16:0/16:0. As lipoproteins modify surfactant metabolism, we postulated an extrapulmonary origin of PC16:0/14:0 enrichment in surfactant. We, therefore, fed rats (d19-26) with trilaurin (C12:0(3)), trimyristin (C14:0(3)), tripalmitin (C16:0(3)), triolein (C18:1(3)) or trilinolein (C18:2(3)) vs. carbohydrate diet to assess their effects on surfactant PC composition and surface tension function using a captive bubble surfactometer. Metabolism was assessed with deuterated C12:0 (ω-d(3)-C12:0) and ω-d(3)-C14:0. C14:0(3) increased PC16:0/14:0 in surfactant from 12 ± 1 to 45 ± 3% and decreased PC16:0/16:0 from 47 ± 1 to 29 ± 2%, with no impairment of surface tension function. Combined phospholipase A(2) assay and mass spectrometry revealed that 50% of the PC16:0/14:0 peak comprised its isomer 1-myristoyl-2-palmitoyl-PC (PC14:0/16:0). While C12:0(3) was excluded from incorporation into PC, it increased PC16:0/14:0 as well. C16:0(3), C18:1(3), and C18:2(3) had no significant effect on PC16:0/16:0 or PC16:0/14:0. d(3)-C14:0 was enriched in lung PC, either via direct supply or via d(3)-C12:0 elongation. Enrichment of d(3)-C14:0 in surfactant PC contrasted its rapid turnover in plasma and liver PC, where its elongation product d(3)-C16:0 surmounted d(3)-C14:0. In summary, high surfactant PC16:0/14:0 during lung development correlates with C14:0 and C12:0 supply via specific C14:0 enrichment into lung PC. Surfactant that is high in PC16:0/14:0 but low in PC16:0/16:0 is compatible with normal respiration and surfactant function in vitro.

Topics: 1,2-Dipalmitoylphosphatidylcholine; Animals; Chromatography, Gas; Chromatography, High Pressure Liquid; Deuterium; Dietary Carbohydrates; Dietary Fats; Female; Lung; Male; Myristic Acid; Phospholipases A2; Pulmonary Surfactants; Rats; Rats, Sprague-Dawley; Respiration; Spectrometry, Mass, Electrospray Ionization; Surface Tension; Tandem Mass Spectrometry; Time Factors; Triglycerides; Triolein

Two simple experiments measuring the 13C linewidths nu(1/2) and spin-lattice relaxation times T(1) of each of the signals in the spectrum of trilinolein indicate that the nu(1/2) and T(1) values are consistent with the different degrees of motional freedom expected for the various 13C nuclei. However, for each chain, the nu(1/2) and T(1) measurements indicate a small reversal in mobility at C-10 relative to C-9 before motional freedom again steadily increases on each chain starting at C-11. The T(1) experiment allows unambiguous assignments of the C-8 signal and C-14 signal, which differ by only 0.010 ppm. Measurements of 13C nu(1/2) and T(1) values on tripalmitin provide secure assignments for the C-5 and C-6 signals, for which conflicting assignments have been reported. The T(1) measurements also show that among the tightly clustered C-8 through C-12 signals, the C-11 signals are the most downfield, while the C-12 signals are the most upfield, again contrary to a previous report. Similar measurements of 13C nu(1/2) and T(1) values on other triacylglycerols or related compounds may prove equally useful in making chemical shift assignments and detecting any discontinuities in motional freedom along a chain. The benefits and possible limitations of ultrahigh field NMR for studying triacylglycerols and related compounds are discussed.

Topics: Carbon Isotopes; Magnetics; Nuclear Magnetic Resonance, Biomolecular; Triglycerides

The effect of dietary fat on hepatic microsomal triglyceride transfer protein(MTP) large subunit mRNA levels in the hamster was examined. Increasing the dietary fat concentration from 11.7 energy % to 46.8 energy % caused a 60% increase in hepatic MTP mRNA; this increase was shown to be dose-dependent (r = 0.688 p = 0.0023). MTP mRNA levels correlated significantly with several plasma lipoprotein cholesterol parameters. No significant relationship was observed between MTP mRNA and either plasma or VLDL triglyceride. The nature of the dietary fatty acids also influenced MTP mRNA levels, with trimyristin and tripalmitin enriched diets significantly elevating MTP mRNA relative to diets enriched in triolein and trilinolein.

Topics: Animals; Carrier Proteins; Cholesterol Ester Transfer Proteins; Cricetinae; Dietary Fats; Energy Intake; Gene Expression Regulation; Glycoproteins; Male; Mesocricetus; Microsomes, Liver; RNA, Messenger; Triglycerides; Triolein

Orlistat, a selective inhibitor of gastrointestinal lipases, was used to investigate triacylglycerol absorption. Using mice and a variety of emulsified dietary lipids we found that the absorption of radiolabelled tripalmitin (containing the fatty acid 16:0), but not of triolein (18:1n-9) or tri-gamma-linolenin (18:3n-6), was incomplete from meals rich in esterified palmitate. Further, the absorption of radiolabelled tri-gamma-linolenin, from both saturated and unsaturated dietary triacylglycerols, was 1.3- to 2-fold more potently inhibited by orlistat than that of triolein and tripalmitin. These radiolabelled triacylglycerols, which have the same fatty acid in all three positions, may not always be accurate markers of the absorption of dietary triacylglycerols. Orlistat was more effective at inhibiting the absorption of radiolabelled triacylglycerols with which it was codissolved than those added separately, which indicates that equilibration between lipid phases in the stomach may not always be complete. The saturation of the dietary lipid had little or no effect on the potency of orlistat. Orlistat provides a novel approach for studying the role of triacylglycerol hydrolysis in the overall process of triacylglycerol absorption.

Topics: Animals; Carbon Radioisotopes; Dietary Fats; Female; Hydrolysis; Intestinal Absorption; Lactones; Lipase; Mice; Mice, Inbred Strains; Orlistat; Triglycerides; Triolein