Ontogenesis of lipids in chick embryo retina

Metabolic fates of yolk lipid and individual fatty acids during embryonic development of the coot and moorhen

There is currently little information regarding the metabolic fates of yolk lipid and individual fatty acids during embryonic development of free-living avian species. Here we report the pattern of lipid utilization during embryonic development of the coot (Fulica atra) and the moorhen (Gallinula chloropus), two related species producing precocial offspring from eggs with a distinctive fatty acid composition and with an incubation period similar to that of the chicken. By the time of hatching, the proportions of the initial yolk lipid that had been transferred to the embryo were 88.2% and 79.8% for the coot and moorhen respectively. During the whole incubation period, 42.9% and 40.0% of the initial yolk lipid of the coot and moorhen respectively were lost from the system due to oxidation for energy, equating to 47.8% and 50.0% respectively of the actual amount of lipid transferred over this time. Thus, the lipid received by the embryos of both species is partitioned almost equally between the alternative fates of energy metabolism and incorporation into tissue lipids. In the coot, this 50:50 split between oxidation and tissue formation was maintained during the hatching process. The proportions of arachidonic (20:4n-6) and docosahexaenoic (22:6n-3) in the yolk lipids of these species were 2.5-3.5 times higher than in eggs of domestic poultry. In contrast to the situation in the chicken, there was no preferential uptake of 22:6n-3 from the yolk during coot and moorhen development. The fatty acid compositions of the whole body lipids of the coot and moorhen hatchlings were almost identical to those of the initial yolks indicating that, unlike the chicken, these species display relatively little overall biomagnification of 20:4n-6 and 22:6n-6 during development. It is suggested that the yolk fatty acid profiles of the coot and moorhen are particularly well matched to the requirements of the embryo, reducing the need for selective uptake of 22:6n-3 and for the overall biomagnification of 22:6n-3 and 20:4n-6.

Alcohol-Induced Lipid and Morphological Changes in Chick Retinal Development

BACKGROUND

Alcohol exposure causes alterations in the lipid content of different organs and a reduction of long-chain fatty acids. During embryo development, the central nervous system is extremely vulnerable to the teratogenic effects of alcohol, and the visual system is particularly sensitive.

METHODS

White Leghorn chick embryos were injected with 10- and 20-microl alcohol doses into the yolk sac at day 6 of incubation. The lipid composition of the retina was analyzed in embryos at day 7 of incubation (E7), E11, E15, and E18. The percentages of phospholipids, free cholesterol, esterified cholesterol, diacylglycerides, and free fatty acids were estimated by using an Iatroscan thin layer chromatography flame ionization detector. Gas chromatography and mass spectrometry were used to determine fatty acid composition. The morphological study was performed at E7, E11, and E19 by means of semithin and immunohistochemical techniques.

RESULTS

In the retina, alcohol causes the total lipid content to change, with a remarkable increase in free cholesterol and a dramatic decrease in esterified cholesterol. Diacylglycerides and free fatty acids tend to increase. Phosphatidylcholine and phosphatidylethanolamine decrease, whereas phosphatidylserine, sphingomyelin, and phosphatidylinositol increase. The main fatty acids of the retina also undergo changes. At E7, myriotic acid increases, and oleic acid and polyunsaturated fatty acids such as arachidonic acid and docosahexaenoic acid decrease. From E18 onward, there is some recovery, except for fatty acids, which recover earlier. From a morphological point of view, alcohol effects on retinal development are various: increase of intercellular spaces in all cell layers, pyknosis with loss of cellularity in the inner nuclear cell layer and ganglion cell layer, retarded or disorderly cell migration, early cell differentiation, and loss of immunoreactivity for myelin oligodendrocyte-specific protein.

CONCLUSIONS

Acute alcohol exposure during embryo development causes the lipid composition of the retina to change, with a trend to recovery in the last stages. These alterations are in line with the changes observed at a morphological level.

The protective role of squalene in alcohol damage in the chick embryo retina

The developing CNS, and in particular the visual system, is very sensitive to the effects of alcohol. Alcohol causes lipid peroxidation. Squalene, the major olive oil hydrocarbon, is a quencher of singlet oxygen and prevents the corresponding lipid peroxidation. We presumed that squalene can protect against the alcohol-induced damage already observed during the development of the chick retina. Alcohol+squalene was administered directly into the yolk sac of the egg of White Leghorn chicks at day 6 of incubation. The lipid composition of the retina was analyzed in embryos at E7, E11, E15 and E18. The proportions of phospholipids, free and esterified cholesterol, diacylglycerides and free fatty acids were estimated using the Iatroscan TLC/FID procedure. Gas chromatography and mass spectrometry were used to determine the fatty acid composition. The morphological study was carried out at E11 using semithin sections, and by means of immunohistochemical techniques at E19. Comparing the results obtained in control embryos, the administration of alcohol+squalene reduces the effects of alcohol on the total lipid composition of the retina during development. The effects were, in fact, of less magnitude than in embryos treated only with alcohol. The major phospholipid species of alcohol+squalene-treated embryos exhibited total recuperation at E15. As far as fatty acids are concerned, no significant changes were observed with regard to control embryos during development. From a morphological point of view, the retinas of alcohol+squalene-treated embryos show at E11 fewer cellular alterations than the retinas of alcohol-treated embryos. In this respect, the retinas of alcohol+squalene-treated embryos exhibited: a columnar cell arrangement similar to that observed in control retinas; few pycnotic cells and very few alterations in ganglion cell layers and in the optic nerve fibers layer. At E19 the recuperation of the expression of myelin oligodendrocyte specific protein (MOSP) in alcohol+squalene-treated embryos was recorded. Since squalene reduces the deleterious effects caused by alcohol on the lipid composition and the structure of the retina, squalene could act as a naturally occurring agent for the prevention of damage caused by abusive alcohol ingestion during pregnancy.

The effect of tyrosol, hydroxytyrosol and oleuropein on the non-enzymatic lipid peroxidation of rat liver microsomes

The effects of the polyphenolic compounds from virgin olive oil: tyrosol, hydroxytyrosol and oleuropein on the non-enzymatic lipid peroxidation induced by ascorbate-Fe2+ of rat liver microsomes were examined. The inhibition of light emission (maximal induced chemiluminescence) by oleuropein was concentration dependent. Hydroxytyrosol showed a substantial degree of inhibition against ascorbate-Fe2+ induced lipid peroxidation in rat liver microsomes that was at least 6 times higher than that observed in the presence of oleuropein. Inhibition of lipid peroxidation by tyrosol was not observed. In rat liver microsomes incubated alone or in the presence of tyrosol, the fatty acid composition was profoundly modified when subjected to in vitro peroxidation mediated by ascorbate-Fe2+, with a considerable decrease of 18:2n6 and 20:4n6; however, changes in fatty acid composition were not observed when microsomes were incubated with hydroxytyrosol. When oleuropein was used at low concentration (5, 15 microM) a considerable decrease of 20:4n6 was observed, but 18:2n6 was not modified; at higher concentration (30, 60 microM) changes in fatty acid composition were not observed. There was a very good correlation between the presence of oxidized phospholipids and the changes in polyunsaturated fatty acids previously observed. Thus, hydroxytyrosol showed the highest protection again oxidized phospholipid formation. The presence of oleuropein at low concentration (5, 15 microM) does not prevent the formation of oxidized phospholipids (8.02 +/- 1.22 and 1.22 +/- 1.22) but concentration higher than 30 microM avoids completely the formation of this molecules whereas tyrosol at any concentration assayed was found to be ineffective and allows the formation not only of oxidized phospholipids but also of oxidized cholesterol.

Fatty acids and squalene carried by alpha fetoprotein, and fetal and adult serum albumin from chicken. Comparison with these from mammals

Alpha fetoprotein (C-AFP), serum albumin (C-fSA) from chicken embryos, and SA from hens were purified using gentle chromatographic and electrophoretic methods, and their fatty acids (FAs) and squalene contents were analyzed using gas chromatography and mass spectrometry. In 7-day-old chick embryo, AFP carries 16% and fSA 6% free FAs, the rest being carried as phospholipids, which differs from rat and pig AFP, where all fatty acids are carried like free fatty acids. At this stage C-AFP contains 3.6% arachidonic acid, which falls to 1.7% in 14-day-old embryos. Both of these figures are significantly lower than in humans, rats, calves, and pigs. C-AFP does not transport docosahexaenoic acid, in notable contrast to the mammals mentioned above. The finding of squalene in the two fetal proteins is reported for the first time. During the interval between 7 and 14 days, the proportion of C16:1 n-7 and of C18:2 n-6 increases 10-fold, that of C18:0 quadruples, and that of C18:1 n-9 decreases 3-fold. Squalene increases in this period from 2.2% to 10.0%. The C-fSA of a 7-day-old embryo transports only one FA with more than two unsaturated carbons, arachidonic acid (2.4%). It also contains squalene (1.2%). Similarly, only arachidonic acid (2.5%), but not squalene is found in hen SA. The percentage of saturated and monounsaturated FAs divided by the percentage of polyunsaturated FAs, and the ratios of the percentage of FAs with C14-C18 with respect to those with C20-C22 transported by C-AFP are very different from those of studied mammals.

Simultaneous quantitation of ceramides and 1,2-diacylglycerol in tissues by Iatroscan thin-layer chromatography-flame-ionization detection

Ceramides and 1,2-diacylglycerol have been demonstrated in intracellular signaling pathways. A method of simultaneous mass determination of ceramides and 1,2-diacylglycerol in tissues was developed using the latroscan which combines thin layer chromatography and flame ionization detection (TLC/FID) techniques. Because of relatively low amounts of these components in tissues, the fraction of nonpolar lipids, which included ceramides and glycerides, was eluted with chloroform/acetone mixture (3:1, vol/vol) through a silicic acid column to eliminate the polar phospholipids. Development of Chromarods was carried out using three solvent systems in a four-step development technique. The relationship of the peak area ratio to weight ratio compared with cholesteryl acetate added as an internal standard was linear. The amount of ceramides increased with incubation of rat heart homogenate and human erythrocyte membranes in the presence of sphingomyelinase (E.C. 3.1.4.12). The latroscan TLC/FID system provided a quick and reliable assessment of ceramides and 1,2-diacylglycerol.