Lysophosphatidylcholine as a preferred carrier form of docosahexaenoic acid to the brain.

The metabolic fate of docosahexaenoic acid (DHA) was evaluated from its intake as a nutrient in triglycerides and phosphatidylcholines to its uptake by target tissues, especially the brain. Several approaches were used including the kinetics and tissue distribution of ingested 13C-labeled DHA, the incorporation of radiolabeled DHA injected as its nonesterified form compared to the fatty acid esterified in lysophosphatidylcholine (lysoPC), and the capacity of the two latter forms to cross a reconstituted blood-brain barrier (BBB) consisting of cocultures of brain-capillary endothelial cells and astrocytes. The results obtained allow us to raise the hypothesis that lysoPC may represent a preferred physiological carrier of DHA to the brain.

Erythrocyte fatty acid composition in term infants fed human milk or a formula enriched with a low eicosapentanoic acid fish oil for 4 months.

UNLABELLED: When term infants are fed standard formula that does not contain long-chain polyunsaturated fatty acids (LC-PUFA), they still show lower levels of docosahexaenoic acid (DHA) in red blood cell (RBC) phospholipids by several weeks or months postnatally. This study was designed in order to evaluate a potential alternative for supplementing term infant formulas with DHA by adding a high-DHA/low-eicosapentanoic acid fish oil to levels similar to that in human milk (0.3%). A total of 37 term infants were included in the study at 3 days of life. DHA concentrations remained stable between inclusion and 4 months of life at around 8% of the RBC phospholipids in the LC-PUFA enriched formula-fed group whereas it decreased significantly in the standard formula-fed group. In the human milk-fed group, RBC DHA concentrations at 4 months of age were significantly lower than that at birth and were significantly correlated with the duration of breast feeding (r = 0.85; P = 0.0002). A significant decrease of arachidonic acid between inclusion and 4 months of age was observed in the enriched formula-fed group and reached a mean value at 4 months, which was significantly lower than that observed in the human milk or standard formula-fed groups (P<0.0001). CONCLUSION: Supplementing term formulas with a high-docosahexaenoic acid/low-eicosapentanoic acid fish oil up to 4 months of age is efficient in improving docosahexaenoic acid status, however it increases the risk of impaired n-6 fatty acid status.

A state of mind in the garden.

SUMMARY Nicole Brossard reflects on the writing process in relation to self, narrative voice, language, translation, lesbian desire and sexuality, genre-blurring, memory, and the cultural milieu. She explores her resistant negotiations of traditional autobiographical modes of writing.

Characterization of plasma unsaturated lysophosphatidylcholines in human and rat.

Unsaturated lysophosphatidylcholines (lysoPtdCho) bound to albumin circulate in blood plasma and seem to be a novel transport system for carrying polyunsaturated fatty acids (PUFA) to tissues that are rich in these fatty acids, such as the brain. The potential of these lysoPtdCho as a significant source of PUFA for cells has been assessed by comparing their plasma concentration with that of unsaturated non-esterified fatty acids (NEFA) bound to albumin. In humans, the PUFA concentration was 25.9+/-3.1 nmol/ml for these lysoPtdCho, compared with 33.4+/-9.6 nmol/ml for NEFA; in rats the equivalent values are 14.2+/-0.6 and 13.1+/-1.1 nmol/ml respectively (means+/-S.E.M.). The lysoPtdCho arachidonic acid content was 2-fold (human) and 5-fold (rat) higher than that of NEFA. In human and rat plasma, unsaturated lysoPtdCho were associated mainly with albumin rather than lipoproteins. The rate and extent of the acyl group shift from the sn-2 to sn-1 position of these lysoPtdCho were studied by the incubation of 1-lyso, 2-[(14)C]C(18:2)n-6-glycerophosphocholine (GPC) with plasma. The rapid isomerization of this lipid occurred at pH 7 (20% isomerization within 2 min) and was not prevented by its association with albumin. The position of the acyl group in the lysoPtdCho circulating in plasma was studied by collecting blood directly in organic solvents containing 1-lyso,2-[(14)C]C(18:2)n-6-GPC as a marker of isomerization that occurred during sampling and analysis. Approx. 50% of the PUFA was located at the sn-2 position, demonstrating that substantial concentrations of 2-acyl-lysoPtdCho are present in plasma and are available for tissue uptake, where they can be reacylated at the sn-1 position to form membrane phospholipids.

Genome structure and gene content in protist mitochondrial DNAs.

Although the collection of completely sequenced mitochondrial genomes is expanding rapidly, only recently has a phylogenetically broad representation of mtDNA sequences from protists (mostly unicellular eukaryotes) become available. This review surveys the 23 complete protist mtDNA sequences that have been determined to date, commenting on such aspects as mitochondrial genome structure, gene content, ribosomal RNA, introns, transfer RNAs and the genetic code and phylogenetic implications. We also illustrate the utility of a comparative genomics approach to gene identification by providing evidence that orfB in plant and protist mtDNAs is the homolog of atp8 , the gene in animal and fungal mtDNA that encodes subunit 8 of the F0portion of mitochondrial ATP synthase. Although several protist mtDNAs, like those of animals and most fungi, are seen to be highly derived, others appear to be have retained a number of features of the ancestral, proto-mitochondrial genome. Some of these ancestral features are also shared with plant mtDNA, although the latter have evidently expanded considerably in size, if not in gene content, in the course of evolution. Comparative analysis of protist mtDNAs is providing a new perspective on mtDNA evolution: how the original mitochondrial genome was organized, what genes it contained, and in what ways it must have changed in different eukaryotic phyla.

The Organelle Genome Database Project (GOBASE).

The taxonomically broad organelle genome database (GOBASE) organizes and integrates diverse data related to organelles (mitochondria and chloroplasts). The current version of GOBASE focuses on the mitochondrial subset of data and contains molecular sequences, RNA secondary structures and genetic maps, as well as taxonomic information for all eukaryotic species represented. The database has been designed so that complex biological queries, especially ones posed in a comparative genomics context, are supported. GOBASE has been implemented as a relational database with a web-based user interface (http://megasun.bch.umontreal.ca/gobase/gobas e.html ). Custom software tools have been written in house to assist in the population of the database, data validation, nomenclature standardization and front-end design. The database is fully operational and publicly accessible via the World Wide Web, allowing interactive browsing, sophisticated searching and easy downloading of data.

Human plasma albumin transports [13C]docosahexaenoic acid in two lipid forms to blood cells.

Docosahexaenoic acid (22:6) decreases blood platelet function and is highly concentrated in the brain where its depletion leads to functional impairments. Because the platelets and blood brain barrier capillary endothelium cannot hydrolyze the complex lipids for fatty acid (FA) uptake, nonesterified FA (NEFA) bound to albumin are assumed to be the delivery route of FA to these cells. The supply of 13C-labeled 22:6 to blood cells by plasma albumin was studied in humans after a single ingestion of this FA esterified in a triglyceride (TG). The 22:6 13C/12C ratio, measured by gas chromatography combustion-isotope ratio mass spectrometry was measured in lipid classes from albumin, platelets, leukocytes, and erythrocytes (taken as a tentative index of the brain uptake). Nonesterified [13C]22:6 bound to albumin was rapidly produced after ingestion, as a result of the hydrolysis of very low density lipoprotein (VLDL) plus chylomicron TG. We found that albumin carried another source of 22:6, lyso-phosphatidylcholines (lyso-PC), in which [13C]22:6 accumulated while the nonesterified [13C]22:6 reached its minimal plasma concentrations. Computation of the relative contribution of NEFA and lyso-PC for the [13C]22:6 delivery to platelets and erythrocytes showed that the [13C]22:6 supply to platelets occurred uniquely through NEFA, whereas this pool was weakly involved in the delivery to erythrocytes. In contrast, lyso-PC was uniquely concerned with the 22:6 delivery to erythrocytes and represented the major part of this supply. We conclude that plasma albumin carries 22:6 in two lipid forms that are involved differently in the delivery of this FA to target cells.

Retroconversion and metabolism of [13C]22:6n-3 in humans and rats after intake of a single dose of [13C]22:6n-3-triacylglycerols.

The apparent retroconversion of docosahexaenoic acid (22:6n-3) to eicosapentaenoic acid (20:5n-3) and docosapentaenoic acid (22:5n-3) was studied in vivo, in rats and humans, after they ingested a single dose of triacylglycerols containing [13C]22:6n-3 ([13C]22:6-triacylglycerol), without 22:6n-3 dietary supplementation. The amount of apparent retroconversion and the distribution of the three n-3 polyunsaturated fatty acids (PUFAs) in plasma lipid classes were followed as a function of time by measuring the appearance of 13C in these PUFAs with gas-chromatography combustion-isotope ratio mass spectrometry. This [13C]22:6n-3 retroconversion, calculated by summing the amounts of [13C]22:5n-3 and [13C]20:5n-3 in plasma lipids, was lower in humans than in rats, reaching a maximum of approximately 9% of the total plasma [13C]22:6n-3 in rats, but only 1.4% in humans. The incorporation of [13C]22:6n-3 and [13C]22:5n-3 in lipid classes followed their endogenous distribution with a maximal accumulation in phospholipids, but a low incorporation into cholesterol esters (CEs), whereas [13C]20:5n-3 was equally present in phospholipids and CEs. The ratio of the amount of HDL-CE to HDL-phosphatidylcholine for [13C]20:5n-3 was higher than for [13C]22:6n-3, indicating a selectivity of the lecithin-cholesterol acyltransferase enzyme with regard to these PUFAs, which may be related to the differences in their biological properties after fish oil feeding. The occurrence of a weak basal 22:6n-3 retroconversion in humans supports feeding this pure PUFA in cases in which 20:5n-3 presents undesirable side effects and when specific alterations of blood lipids are expected.

Metabolic fate of an oral tracer dose of [13C]docosahexaenoic acid triglycerides in the rat.

The appearance of 13C in rat lipoprotein, blood cells, and brain lipids was followed as a function of time after the ingestion of triglycerides (TG) containing [13C]22:6n-3. The time course of 13C abundance in 22:6n-3 of various lipid pools, measured by gas chromatography combustion-isotope mass spectrometry, established precursor-product relationships within lipids. The [13C]22:6n-3 was rapidly incorporated into very low density lipoprotein-chylomicron-TG and unesterified fatty acids bound to albumin, with a concomitant maximal appearance at 3 h and further decline. Lysophosphatidylcholines (lysoPC) bound to albumin were also enriched in [13C]22:6n-3, and their labeling appeared to be mainly due to hepatic secretion at the earliest time points. From 12 h postingestion, the synthesis of [13C]22:6n-3-lysoPC was twice as high as that of unesterified [13C]22:6n-3, making lysoPC a potential source of 22:6n-3 supply for tissues. The labeling of platelets, red blood cells, and brain phospholipids presented different kinetics, presumably involving the two lipid forms of [13C]22:6n-3 bound to albumin, to different extents. We conclude that [13C]22:6n-3 esterified in TG is rapidly redistributed within blood lipoproteins and the albumin fraction and that its incorporation in lipid species bound to albumin influences its uptake by target tissues.

In vivo compartmental metabolism of 13C-docosahexaenoic acid, studied by gas chromatography-combustion isotope ratio mass spectrometry.

The exchange of docosahexaenoic acid (22:6n-3) within lipid pools in rat and human has been followed as a function of time after the ingestion of triglycerides (TG) containing 22:6n-3 labeled with 13C(13C 22:6n-3). The 13C abundance in the fatty acid was measured by gas-chromatography-combustion isotope ratio mass spectrometry which allowed the detection of 0.001 atom 13C percent 12C. The 13C 22:6n-3 appearance was rapid in the TG of very low density lipoprotein plus chylomicron fraction, in which the maximal labeling was observed at 3 and 2 h after ingestion in rat and human, respectively. Concomitant with the TG utilization of this fraction by lipoprotein lipase from tissues, unesterified 13C 22:6n-3 appeared in the plasma albumin. 13C 22:6n-3 bound to albumin was mostly present in unesterified form before 12 h post-ingestion while after that period, lysophosphatidylcholine (lysoPC) bound to albumin carried higher 13C 22:6n-3 concentrations. These lyso-PC were mostly from hepatic origin and might represent a potential source of 22:6n-3 redistribution to tissues. The 13C 22:6n-3 uptake into rat brain PC and phosphatidylethanolamine was still increasing when the concentration of plasma unesterified 13C 22:6n-3 had already dropped to a minimal plateau value and during the period of maximal plasma circulation of 13C 22:6n-3-lysoPC bound to albumin. In contrast, the uptake of 13C 22:6n-3 into blood platelet PC occurred during the phase of important circulation of 13C-22:6n-3 bound to albumin, suggesting the in vivo efficiency of the Lands pathway for this fatty acid. It is concluded that 13C 22:6n-3 esterified in TG is rapidly absorbed and redistributed within plasma lipoproteins and that its redistribution within the two lipid species bound to albumin might influence its uptake by platelets and rat brain.

Stable isotope tracer and gas-chromatography combustion isotope ratio mass spectrometry to study the in vivo compartmental metabolism of docosahexaenoic acid.

A gas-chromatography combustion isotope ratio mass spectrometry (GCC-IRMS) method using carbon 13 (13C)-stable isotope to trace n-3 polyunsaturated fatty acids (PUFA) turnover in vivo is presented. Natural 13C abundance of commercial n-3 PUFA was measured from 100 to 300 ng of fatty acids and was -27.58, -27.83, and -28.16 for 22:6n-3, 22:5n-3, and 20:5n-3, expressed as delta 13C /1000 versus Pee Dee Belemnite (PDB), respectively. Precision of delta 13C /1000 values was comparable for the three PUFA and gave relative standard deviations of 0.95-0.97%. Isotope enrichment of 0.0010 at.% could be detected. Triglycerides enriched in [13C]22:6n-3 ([13C]22:6-TG) were synthesized by growing a microalgae on [1-13C]glucose. [13C]22:6n-3 represented 36 wt.% of total triglyceride fatty acids and had an isotope enrichment of 2.0420 at.%, which was the double of natural abundance. The isotope enrichment of 22:6n-3 in lipids from rat lipoproteins and red cells could be followed as a function of time after ingestion of 3 mg [13C]22:6-TG and showed specific patterns according to the lipid compartments. The retroconversion of [13C]22:6n-3 was also detected in HDL phosphatidylcholine by the appearance of [13C]22:5n-3 and [13C]20:5n-3. On the other hand, 22:6n-3 natural 13C abundance in human lipid classes of lipoproteins and blood cells has been measured using 10 ml plasma, even for the more limiting lipid compartments in terms of 22:6n-3 dose size.(ABSTRACT TRUNCATED AT 250 WORDS)