| Docosahexaenoic acid (DHA) is the most abundant omega-3fatty acid in themammalian brain, accounting for8-14%of fatty acids at perinatally in primates andincluding humans. In humans, DHA accumulates at an accelerating rate from themiddle of gestation reaching an inflection point in the first months after birth andcontinuing well past the plateau of brain weight to plateau at about18years of ageand remain stable through the end of life.DHA can be synthesized de novo by term and preterm human infants fromprecursor omega-3fatty acids, α-linolenic acid (ALA) or eicosapentaenoic acid (EPA)but the process is generally considered to be inefficient on average with currentdietary intakes of omega-6linoleic acid at relatively high levels. Numerous humanstudies show efficacy of dietary preformed DHA for brain and visual development,and follow-up studies show that preformed DHA intake in infancy provides long termbenefits on tests of higher function, though it is widely agreed that the Bayley scales,a widely used test for normalcy, consistently shows no effect.While all preformed DHA is identical, in human foods and foodsupplements.The natural lipid classes that carry most long chain polyunsaturated fattyacids in foods are triacylglycerols (TG) or as phospholipid (PL). In milks, includinghuman breastmilk, DHA is richer in PL than in TAG, but the bulk of DHA is found inTAG because of the overwhelming prevalence of TG over PL. TG-DHA is the mostcommon molecular form used as a component of infant formula, though sources ofthe other long chain polyunsaturated fatty acid in infant formula, arachidonic acid(ARA), are PL. Ongoing development of alternative sources of DHA has identifiedcomponents potentially suitable for use in infant formulas that use PL-DHA. infantformula products were also widely available on the European market before thismarket expanded and changed for single-cell-and fi sh oil-based sources of TG-boundARA and DHA. Different esterified forms of LCPUFA may show different mechanisms ofabsorption, metablism as well as distribution. Previously we showed by13C labelingthat ARA-PL, specifically as phosphatidylcholine (ARA-PC), when added to artificialformula is about twice as efficacious as a substrate for supplying ARA to the brain asARA-TAG in neonatal baboons. We report here a similar study in neonatal pigletsusing13C-DHA and specifically investigating efficacy for supplying the gray matterof the cerebral cortex with DHA.Twenty piglets,2to4days of age, were chosen for the study. Piglets fed on acommercial available formula immediately upon arrival at the study site. On day16oflife,16robust piglets were assigned to two dosing groups balanced with respect togender, weight, and age but otherwise distributed randomly. Group PC were orallydosed with PC-13C-DHA once; Group TG were orally dosed with TG-13C-DHA once.The four smallest piglets were used as natural abundance isotopic controls and did notreceive a dose but were otherwise treated identically to the other groups.Six days afterthe dose, and on a single day after20days of formula, all piglets were euthanized byexsanguination under anesthesia. Blood for fatty acid analysis was collected in tubeswith EDTA and spun to prepare red blood cells. The surface few mm of the graymatter on the cerebral cortex superior surface were rapidly collected at necropsy. Apiece was immediately used for preparation of synaptosomes, and the remaining graymatter was flash frozen for fatty acid analysis. Retina, heart, liver, biceps femorismuscle and kidney were also harvested, and all tissues were flash frozen and stored at-80°C until prepared for analysis. Lipdis were extracted from those sampels and weresubmitted to GC-FID and GC-C-IRMS anaylsis.To investigate the mechanism underlying DHA’s incorpration into CNS, porcinebrain microvascular endothelial cells (PBMEC) were cultured in vitro and DHA atdifferent concentration was added to the cell culture to observe its effect on geneexpression of fatty acids trasfering protein like CD36,FATP.Meanwhile expression ofnuclear transcript factors were also determined.13C label was detected for DHA and22:5n-3(DPAn-3) only among all fattyacids. The highest%Dose was detected in cerebral cortex gray matter in the13C-DHA-PC dosed animals, at about0.37%.13C-DHA from the TAG dose was abouthalf this value, thus dietary PC was1.9-fold more efficacious for supplying DHA tothe developing piglet brain than TAG. Results in gray matter synaptosomes were consistent with the relative values. The ratio of relative accretion of labeled DHA was1.7-fold greater for PC than for TAG. Liver retained6.8%of the PC13C-dosecompared to3.5%of the TAG dose at6days post-dose. The relative efficacy was1.9,similar to the gray matter and synaptosomes.Relative efficacy of PC over TAG is2.2-fold for DHA, and about2.4-fold for DPAn-3, all similar and consistent withresults in other examined tissues including retina, heart, liver, biceps femoris muscle,kidney, plasma and RBC.In summary, stable isotope tracer doses of DHA bound in the sn-2position ofPC was1.9-fold more efficacious for supply of cerebral cortex gray matter than DHAbound to the sn-2position of TAG. These data are generally consistent withnumerous previous measurements on other LCPUFA and on DHA studied in otherspecies. Together with previous work, the results indicate that PC is a highlyefficacious source of both DHA and ARA, the two major LCPUFA of human breastmilk.Incubation PBMEC with DHA showed an increased gene expression of CD36and FATP1. DHA regulated CD36and FATP1via PPARγ. |
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