Quantitative analysis of fatty acids in phospholipids, diacylglycerols, free fatty acids, and other lipids

Characterization of the unique In Vitro effects of unsaturated fatty acids on the formation of amyloid β fibrils

Accumulation of amyloid ß (Aß) peptides, the major component of amyloid fibrils in senile plaques, is one of the main causes of Alzheimer’s disease. Docosahexaenoic acid (DHA) is a fatty acid abundant in the brain, and is reported to have protective effects against Alzheimer’s disease, although the mechanistic effects of DHA against Alzheimer’s pathophysiology remain unclear. Because dietary supplementation of DHA in Aß precursor protein transgenic mice ameliorates Aß pathology and behavioral deficits, we hypothesize that DHA may affect the fibrillization and deposition of Aß. Here we studied the effect of different types of fatty acids on Aß fibril formation by in vitro Aß fibrillization assay. Formation of amyloid fibrils consists of two steps, i.e., the initial nucleation phase and the following elongation phase. We found that unsaturated fatty acids, especially DHA, accelerated the formation of Aß fibrils with a unique short and curved morphology in its nucleation phase, which did not elongate further into the long and straight, mature Aß fibrils. Addition of DHA afterwards did not modify the morphology of the mature Aß(1–40) fibrils. The short and curved Aß fibrils formed in the presence of DHA did not facilitate the elongation phase of Aß fibril formation, suggesting that DHA promotes the formation of “off-pathway” conformers of Aß. Our study unravels a possible mechanism of how DHA acts protectively against the pathophysiology of Alzheimer’s disease.

Organization of NADPH-cytochrome P450 reductase and CYP1A2 in the endoplasmic reticulum--microdomain localization affects monooxygenase function

Cytochrome P450 is part of an electron transport chain found in the endoplasmic reticulum (ER), with its catalytic function requiring interactions with NADPH-cytochrome P450 reductase (CPR). The goals of this study were to examine how the P450 system proteins are organized in the membrane and to determine whether they are distributed in detergent-resistant lipid microdomains (DRM). Isolated liver microsomes from untreated rabbits were treated with 1% Brij 98, and DRMs were isolated via sucrose gradient centrifugation. Lipid analysis showed that DRM fractions were enriched in cholesterol and sphingomyelin, similar to that found with plasma membrane DRMs. Approximately 73% of CYP1A2 and 68% of CPR resided in DRM fractions, compared with only 33% of total ER proteins. These DRMs were found to be cholesterol-dependent: CPR and CYP1A2 migrated to the more dense regions of the sucrose gradient after cholesterol depletion. CYP1A2 function was studied in three purified lipid vesicles consisting of 1) phosphatidylcholine (V-PC), 2) lipids with a composition similar to ER lipids (V-ER), and 3) lipids with a composition similar to the DRM fractions (V-DRM). Each system showed similar substrate binding characteristics. However, when the association between CPR and CYP1A2 was measured, V-ER and V-DRM liposomes produced lower apparent K(m) values compared with V-PC without any significant change in V(max). These findings suggest that CYP1A2 and CPR reside in ER-DRMs and that the unique lipid components of these domains enhance CYP1A2 substrate metabolism through greater efficiency in CPR-CYP1A2 binding.

Effects of hyperglycemia and hypercapnia on lipid metabolism during complete brain ischemia

Ischemic damage is greatly enhanced by preischemic hyperglycemia or hypercapnia, which affects many intracellular responses including protein kinase C (PKC) translocation. We explored whether hyperglycemic or hypercapnic ischemia affects lipid metabolism, especially ischemia-induced release of free fatty acids (FFAs) and diacylglycerols (DAGs). A change in intraischemic level of acidosis was induced either by injecting glucose (hyperglycemic, HG) or by adding CO(2) (hypercapnic, HC). Complete cerebral ischemia was induced, and the brain was frozen in situ after 3, 5, and 10 min at 37 degrees C. Frontoparietal neocortex was dissected for FFA and DAG lipid analysis by thin-layer chromatography and gas-liquid chromatography. Significant differences were shown between normoglycemic and either hypercapnic or hyperglycemic values for individual and total FFAs. A significant delay in the release of FFA in ischemia with hyperglycemia or hypercapnia was observed. Significant differences were also shown in individual DAG-acyl groups and total DAGs. Hyperglycemic or hypercapnic ischemia resulted in a significant decrease of DAG at 10 min of ischemia. This was unexpected because a previous study showed that PKC translocation was significantly enhanced under similar condition at this time point. Upon cellular depolarization, massive influx of calcium and FFA accumulation may decrease the PKC dependence of DAG for translocation. In addition, PKC activation may lead to a negative feedback inhibition of phospholipase C.

Systemic fatty acid responses to transient focal cerebral ischemia: influence of neuroprotectant therapy with human albumin

Human albumin therapy is highly neuroprotective in focal cerebral ischemia. Because albumin is the main carrier of free fatty acids (FFA) in plasma, we investigated the content and composition of plasma FFA in jugular vein (JV), femoral artery (FA) and femoral vein (FV) of rats given intravenous human albumin (1.25 g/kg) or saline vehicle (5 mL/kg) 1 h after a 2 h middle cerebral artery occlusion (MCAo) or sham surgery. Arachidonic acid was the only FFA significantly increased by MCAo in all plasma samples prior to albumin administration, remaining at the same level regardless of subsequent treatments. Albumin treatment induced in both MCAo- and sham-groups a 1.7-fold increase in total plasma FFA (mainly 16:0, 18:1, 18:2n-6) during 90-min reperfusion. MCAo selectively stimulated the albumin-mediated mobilization of n-3 polyunsaturated fatty acids (PUFA), with an early increase in 22:5n-3 and 22:6n-3 in the FA prior to detectable changes in the JV. In the MCAo-albumin group, the lower level of FFA in JV as compared with FA and FV suggests an albumin-mediated systemic mobilization and supply of FFA to the brain, which may favor the replenishment of PUFA lost from cellular membranes during ischemia and/or to serve as an alternative source of energy, thus contributing to albumin neuroprotection.

What synaptic lipid signaling tells us about seizure-induced damage and epileptogenesis

Glutamate, the most abundant excitatory neurotransmitter in the mammalian CNS, plays a central role in many neuronal functions, such as long-term potentiation, which is necessary for learning and memory formation. The fast excitatory glutamate neurotransmission is mediated by ionotropic receptors that include AMPA/kainate and N-methyl-D-aspartate (NMDA) receptors, while the slow glutamate responses are mediated through its interaction with metabotropic receptors (mGluRs) coupled to G-proteins. During seizures, massive release of glutamate underlies excitotoxic neuronal damage as it triggers an overflow of calcium in postsynaptic neurons mediated by NMDA-gated channels. The early upstream postsynaptic events involve the activation of phospholipases, with the release of membrane-derived signaling molecules, such as free arachidonic acid (AA), eicosanoids, and platelet-activating factor (PAF). These bioactive lipids modulate the early neuronal responses to stimulation as they affect the activities of ion channels, receptors, and enzymes; and when released into the extracellular space, they can contribute to the modulation of presynaptic neurotransmitter release/re-uptake, and/or affect other neighboring neuronal/glial cells. The downstream postsynaptic events target the nucleus, leading to activation of gene-expression cascades. Syntheses of new proteins are the basis for seizure-induced sustained physiological and/or pathological changes that occur hours, days, or months later, such as synaptic reorganization and repair, and apoptotic/necrotic neuronal death. The intricate mesh of signaling pathways converging to the nucleus, and connecting upstream to downstream synaptic events, are at present the focus of many research efforts. We describe in this chapter how seizure-induced glutamate release activates the hydrolysis of membrane AA-phospholipids via phospholipase A2 (PLA2), PLC, and PLD, thus releasing bioactive lipids that, in turn, modulate neurotransmission. We discuss mechanisms through which lipid messengers, such as AA and PAF, may turn into injury mediators participating in seizure-induced brain damage.

The turnover of phospholipid fatty acyl chains is activated by the insecticide Dieldrin in Bufo arenarum oocytes

Dieldrin is a widespread environmental contaminant hazardous to many wildlife species. Some evidence obtained with Bufo arenarum oocytes indicates that Dieldrin decreases the fertilization rate in amphibian oocytes, but little is known about mechanisms by which the pesticide affects fertilization. Therefore, we investigated the effect of Dieldrin on oocyte phospholipid metabolism. Freshly obtained oocytes, prelabeled with 2 3H-glycerol or 9-10 3H palmitate, were exposed to 4 mg/L Dieldrin for 2 hours. Dieldrin reduced the amount of 2 3H-glycerol incorporation in all phosphoglycerides classes: PI, PA, PS, and SPH were affected in 80% of the cases and PC and PE were only reduced in 39% of the cases. The incorporation in neutral lipids was not affected. On the contrary, 9,10 3H-palmitate incorporation increased in PC, PI, and PA, but TAG and FFA decreased. The more efficient incorporation of 3H-palmitate compared with 3H-glycerol in Dieldrin-treated oocytes suggests the operation of an alternative route other than de novo synthesis for phospholipids. The retailoring of phosphoglycerides via a deacylation-acylation pathway was demonstrated. These changes in phospholipid metabolism could be associated with the activation of certain enzymes produced by the pesticide.

Strong association of unesterified [3H]docosahexaenoic acid and [3H-docosahexaenoyl]phosphatidate to rhodopsin during in vivo labeling of frog retinal rod outer segments

Docosahexaenoic acid (DHA, 22:6n-3), the most prevalent fatty acid in phospholipids of rod outer segments (ROS), is essential for visual transduction and daily renewal of ROS membranes. We investigated the association of [3H]DHA-lipids to rhodopsin in ROS from frogs (Rana pipiens) after in vitro (4 hrs) and in vivo (1 day and 32 days) labeling. Lipids from lyophilized ROS were sequentially extracted with hexane (neutral lipids), chloroform:methanol (phospholipids) and acidified chloroform:methanol (acidic phospholipids). After in vitro labeling, free [3H]DHA was easily extracted with hexane (66% of total ROS free DHA), implying a weak association with proteins (rhodopsin). In contrast, after in vivo labeling free [3H]DHA was mainly recovered in the acidic solvent extract (89-99%). Of all phospholipids, [3H-DHA]phosphatidic acid (PA) displayed the highest binding to rhodopsin after both in vitro (43% in acidic extract) and in vivo (>70%) labeling suggesting a possible modulatory role of free DHA and DHA-PA in visual transduction.

Cortical impact injury in rats promotes a rapid and sustained increase in polyunsaturated free fatty acids and diacylglycerols

Neurotrauma activates the release of membrane phospholipid-derived second messengers, such as free arachidonic acid (20:4n-6, AA) and diacylglycerols (DAGs). In the present study, we analyze the effect of cortical impact injury of low-grade severity applied to the rat frontal right sensory-motor cortex (FRC) on the accumulation of free fatty acids (FFAs) and DAGs in eight brain areas 30 min and 24 hours after the insult. At these times, accumulation of FFAs and DAGs occurred mainly in the damaged FRC. The cerebellum was the only other brain area that displayed a significant accumulation of DAGs by day one post-injury. By 30 min, accumulation of free AA in the FRC displayed the greatest relative increase (300% over sham value), followed by free docosahexaenoic acid (22:6n-3, DHA, 150%), while both 20:4-DAGs and 22:6-DAGs were increased 100% over sham values. At day one, free 22:6 and 22:6-DAGs showed the greatest increase (590% and 230%, respectively). These results suggest that TBI elicits the hydrolysis of phospholipids enriched in excitable membranes, targeting early on 20:4-phospholipids (by 30 min post- trauma) and followed 24 hours later by preferential hydrolysis of DHA-phospholipids. These lipid metabolic changes may contribute to the initiation and maturation of neuronal and fiber track degeneration observed following cortical impact injury.

Effect of hen age, body weight, and age at photostimulation. 2. Embryonic characteristics of commercial turkeys

Turkey hens from two BW groups (which averaged 11.8 and 12.9 kg, Normal and Heavy, respectively) were photostimulated at either 29 or 31 wk of age to determine how changes in egg weight and egg component weights with hen age affect subsequent embryonic growth and yolk sac lipid mobilization. At 2-wk intervals during the first 10 wk of lay, all eggs were collected, individually weighed, and incubated. A subsample of eggs from each photostimulation (PS) age and BW group were randomly selected for yolk and albumen weight determinations and embryo weight, liver weight, and yolk sac measurements at 21 and 25 d of incubation. Yolk and yolk sac lipid measurements were done on similar sized eggs selected at 4 to 6 and 12 to 14 wk after PS. Yolk-free embryo weight, liver weight, and yolk sac weight at 21 and 25 d of incubation increased during the first 10 wk of lay. Neither hen age nor BW at PS had any consistent effects on yolk-free embryo weight, liver weight, or yolk-sac weight. When similar-sized eggs (80 to 85 g) were selected for analyses, yolk lipid content did not change with hen production age. The lipid content of the yolk sac was 0.97 g greater in 21-d embryos from hens 12 to 14 wk after PS than from hens 4 to 6 wk after PS. Differences in yolk sac residual lipid and lipid subclass characteristics were not evident after 25 d of incubation. In conclusion, hen BW at PS or age at PS had minimal affects on embryonic growth during the last week of incubation, and most differences in embryonic growth were attributed to differences in yolk sac lipid mobilization between hen production ages independent of egg size.

Inclusion of coconut oil in diets for turkey breeders and its effects on embryonic yolk and liver fatty acids

Turkey hens were fed either a standard breeder diet (CON, myristic acid, C14.0, 1.1%; palmitic acid, C16:0, 16.8%; oleic acid, C18:1, 23%; linoleic acid, C18:2, 48.7%) or a diet containing 5% coconut oil (COCO) enriched with medium chain fatty acids (MCFA; lauric acid, C12:0, 22.6%; C14:0, 10.8%; C16:0, 12.5%; C18:1, 14.8%; C18:2, 24.6%). After 10 d on the diets, fresh eggs were collected for yolk lipid and fatty acid (FA) determination. An additional 60 to 95 eggs were incubated and the FA profiles of the neutral lipid (NL) and phospholipid (PL) fractions of yolk sac and liver lipids were determined. The NL fraction of the yolk sac from CON eggs contained less C12:0 (0 vs 0.49%) and C14:0 (0.7 vs 4.6%) and more C18:1 (41.3 vs 37.5%). The PL fraction of the yolk sac from both treatments contained < 1% C14:0, and there was less than a 2% difference between treatments in other FA concentrations. The hepatic NL fraction from both treatments contained < 1% C14:0 and only C18:1 showed > 1% differences between treatments (Control = 59.9%; COCO = 56.62%). There were no dietary effects on the FA profile of hepatic PL. The presence of only minimal quantities of MCFA in hepatic NL and PL suggests that absorbed yolk sac MCFA are extensively metabolized during embryonic development.

Lead disrupts eicosanoid metabolism, macrophage function, and disease resistance in birds

Lead (Pb) affects elements of humoral and cell-mediated immunity, and diminishes host resistance to infectious disease. Evidence is presented supporting a hypothesis of Pb-induced immunosuppression stemming from altered fatty acid metabolism, and mediated by eicosanoids and macrophages (MO). Chronic Pb exposure increases the proportion of arachidonate (ArA) among fatty acids in lipid from avian tissues, and this change provides precursors for eicosanoids, the oxygenated derivatives of ArA that mediate MO acute inflammatory response. In the current study, we showed that the concentration of ArA in phospholipids of MO elicited from turkey poults fed 100 ppm dietary Pb acetate was twice that of controls. In vitro production of eicosanoids by these MO was substantially increased, and this effect was most pronounced following lipopolysaccharide stimulation: prostaglandin F2 alpha was increased 11-fold, thromboxane B2 increased threefold, and prostaglandin E2 increased by 1.5 times. In vitro phagocytic potential of these MO was suppressed, such that the percentage of MO engulfing sheep red blood cell (RBC) targets was reduced to half that of control MO. In vivo susceptibility of Pb-treated and control birds to Gram-negative bacteria challenge was also evaluated. The morbidity of chicks inoculated with Salmonella gallinarum and fed either control or 200 ppm Pb acetate-supplemented diets was similar, except early in the course of the disease when mortality among Pb-treated birds was marginally greater. In these studies, effects of Pb that could influence immunological homeostasis were demonstrated for MO metabolism of ArA, for production of eicosanoids, and for phagocytosis. There was also the suggestion that these in vitro indices of immune function are related to in vivo disease resistance.

Changes in fatty acid profiles in different lipid classes during late development of turkey embryos from two genetic lines

Fatty acid (FA) profiles in embryonic yolk sacs (YS) and livers were studied in embryos from a randombred turkey line (RBC2) and a line selected for body weight at 16 wk (F line). There were no differences in FA profiles of fresh yolk lipids. During the course of incubation, oleic acid (C18:1) was higher and linoleic acid (C18:2) was lower in YS triglyceride (TG) and phospholipid (PL) subclasses in F line compared with RBC2 embryos. In both lines, the C18:1 content of YS cholesteryl esters (CE) increased from 58 to 63% during the last 6 d of incubation. From 22 to 28 d of incubation, there was a constant C18:1 concentration in hepatic CE, which was > 60% of total hepatic CE FA. As incubation proceeded, palmitic acid (C16:0) and C18:1 in hepatic TG decreased from 27 to 16% and 37 to 34%, respectively. The stearic acid (C18:0) in TG increased from 12% at Day 22 to 32% of total FA at hatch (Day 28) in RBC2 embryos compared with a lesser increase in the F line (11.8 to 18.6%). In hepatic PL, arachidonic acid (C20:4) decreased, whereas both C16:0 and C18:0 increased from 22 to 28 d of incubation. During this same time period, there was an overall decline in docosahexaenoic acid (C22:6) only in the RBC2. On Days 26 and 28, F line embryos had greater concentrations of C22:6 and C20:4 in hepatic PL than did RBC2. These results suggest that selection for increased BW has changed the proportional incorporation of different FA into embryonic lipids.

Post-Golgi vesicles cotransport docosahexaenoyl-phospholipids and rhodopsin during frog photoreceptor membrane biogenesis

Post-Golgi vesicles budding from the trans-Golgi network (TGN) are involved in the vectorial transport and delivery of rhodopsin to photoreceptor rod outer segments (ROS). We report here that newly synthesized docosahexaenoyl (DHA) phospholipids are sequestered and cotransported by rhodopsin-bearing post-Golgi vesicles to ROS. Frog retinas were pulse-labeled with [35S]methionine/cysteine and [3H]DHA prior to ROS isolation and subcellular fractionation. After a 1-h pulse, relatively uniform [3H]DHA-lipid labeling (DPM/microg protein) was observed in all fractions enriched in post-Golgi vesicles, TGN, Golgi, and endoplasmic reticulum (ER) membranes. During the subsequent 2-h chase translocation of free [3H]DHA from ROS to the photoreceptor inner segment contributed to an additional overall increase in labeling of lipids. The specific activity (dpm/nmol DHA) in ER-enriched fraction was similar or higher than in other subcellular fractions after both the pulse and the chase, indicating that the bulk of [3H]DHA-lipids was synthesized in the ER. After the chase a 2-fold increase in labeling of lipids in the ER and Golgi and a 2.6-fold in lighter TGN-enriched fractions was observed. The highest labeling was in the post-Golgi vesicle fraction (4-fold increase), with [3H]DHA-phosphatidylcholine and [3H]DHA-phosphatidylethanolamine showing the greatest increase. At the same time, newly synthesized [35S]rhodopsin shifted from the ER and Golgi toward TGN and post-Golgi fractions. Therefore, sequestration and association of [35S]rhodopsin and [3H]DHA-lipids in a TGN membrane domain occurs prior to their exit and subsequent vectorial cotransport on post-Golgi vesicles to ROS. Labeling of ROS lipids was very low, with phosphatidylinositol and diacylglycerols displaying the highest labeling. This indicates that other mechanisms by-passing Golgi, i.e. facilitated by lipid carrier proteins, may also contribute to molecular replacement of disc membrane DHA-phospholipids, particularly phosphatidylinositol.

Retinal fatty acids of piglets fed docosahexaenoic and arachidonic acids from microbial sources

Docosahexaenoic acid (DHA, 22:6n-3) and arachidonic acid (AA, 20:4n-6) serve important roles in perinatal visual and neural development. A neonatal pig model was used to determine if dietary supplementation with DHA and AA at slightly greater concentrations than normally found in human milk would influence fatty acid accretion in retina. One-day-old piglets were assigned to one of four diets (n = 5/group): (i) STD, standard diet containing fat similar to infant formula; (ii) STD + DHA, 0.7% of fatty acids as DHA; (iii) STD + AA, 0.9% as AA; and (iv) STD + BOTH, 0.8% as DHA plus 1.0% as AA. After 25 d, fatty acids in retina phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were determined. Supplementation with DHA resulted in approximately twofold increases (P < 0.05) in PC-DHA (4.88% in STD vs. 10.03% in STD + DHA and 9.47% in STD + BOTH). Similarly, AA supplementation increased PC-AA 1.3-1.4-fold (4.47% in STD vs. 6.19% in STD + AA and 5.70% in STD + BOTH). For PE, supplementation with either fatty acid or in combination resulted in no significant increases, except for a 1.2-fold increase in DHA for STD + BOTH (32.66%) vs. STD (28.38%). Thus, PC responded to dietary supplementation, with addition of DHA, AA, or BOTH, resulting in increases in respective fatty acids; PE was less responsive, with only STD + BOTH resulting in increased DHA. No significant competition between DHA and AA in incorporation into phospholipids was observed. In conclusion, consumption of a combination of DHA and AA by neonatal pigs supported accretion of DHA in retina phospholipids, while simultaneously supplying the AA necessary for membrane phospholipids and eicosanoid biosynthesis.

Alterations in rabbit retina lipid metabolism induced by detachment. Decreased incorporation of [3H]DHA into phospholipids

BACKGROUND

Docosahexaenoic acid (22:6n-3, DHA) is found in high concentration in phospholipids from retinal membranes, and is essential for their function. This study investigated the effect of in vivo retinal detachment on in vitro lipid metabolism using [3H]DHA.

METHODS

Rabbit retina was detached from the retinal pigment epithelium by injecting physiological saline into the subretinal space of the eye. Retinal samples from control (non-operated) and sham (operated, no detachment) animals, and from attached and detached retinal areas from the same eye, were incubated in vitro with [3H]DHA for 4 hours, and then prepared for biochemical and autoradiographic analysis.

RESULTS

In control and sham retinas, [3H]DHA was preferentially esterified into phospholipids (82%) with low labeling of free fatty acids (FFA) (5%). In samples from detached areas of the retina, a higher proportion of [3H]DHA was recovered in the FFA pool (up to 30%) and its esterification was shunted into triacylglycerol, thereby reducing the formation of [3H]DHA-phospholipids. Changes were sustained through 48 hours of postdetachment. High labeling of inner segments and synaptic terminals was observed autoradiographically in control retinas, while in detached retinas, clusters of labeling were detected in the neural retina, and eventually within the photoreceptor layer.

CONCLUSION

Retinal detachment induces longlasting changes in lipid metabolism which are reflected in lower labeling of [3H]DHA-phospholipids. Metabolic changes, sustained through 48 hours, may lead to inadequate synthesis/turnover of phospholipids, among them, those containing DHA, possibly resulting in defective disc membrane assembly with subsequent deterioration of visual cells.

The concentration of different lipid classes during late embryonic development in a randombred turkey population and a subline selected for increased body weight at sixteen weeks of age

Lipid changes in the yolk sac of the embryo were studied in a randombred population of turkeys (RBC2) and a subline of the RBC2 selected for increased BW at 16 wk (F line). Comparisons of yolk sac and embryonic development were made between 22 d of incubation and hatch (28 d). Poults from the F line had heavier yolk sacs from 24 to 28 d and yolk free body weight was also heavier at hatch (61.1 vs 52.8 g). Yolk sac lipid (percentage of DM) declined faster in F line embryos (69 to 39%) compared with the RBC2 line (62 to 48%). In both lines, embryonic liver dry matter and lipids (percentage of DM) were similar. Yolk sac neutral lipids increased from 22 to 28 d (70 to 80% total lipid) in both lines and there was a concomitant decline in phospholipids (30 to 20%). The direction of the changes was similar for embryonic liver lipid. At 26 and 28 d, there were significantly increased neutral lipids (94 vs 88%) and decreased phospholipids (6 vs 12%) in RBC2 compared with F line embryonic livers. The concentration of cholesterol esters (percentage of total lipid) increased in the yolk sac and embryonic liver during the course of incubation. At 26 and 28 d, livers from RBC2 embryos had increased cholesterol ester concentration compared with livers from the F line.(ABSTRACT TRUNCATED AT 250 WORDS)

Membrane lipid degradation is related to interictal cortical activity in a series of seizures

Brain levels of free fatty acids (FFA) and diacylglycerols (DAG) rise rapidly with the onset of seizures, reflecting activation of phospholipases A2 (PLA2) and C (PLC), respectively. However, the ictal/interictal accumulation of FFA attenuates as recurrent seizures continue. To assess the role of neuronal activity in stimulating PLA2 and C, we compared FFA and DAG in rat cerebral cortex during recurrent ictal periods as a function of associated levels of interictal activity. Pentobarbital-anesthetized rats were paralyzed, ventilated with 30% O2 and subjected to periodic pentylenetetrazol seizures at intervals of 5 min. Animals were killed with focused-microwave irradiation during either the 3rd or 15th seizure. The rise in cortical FFA levels during early seizures for 20:4, 22:6, and 18:0 was 3.6-, 2.5-, and 2.2-fold greater, respectively, when adjacent interictal activity was intense as compared to weak activity. During late seizures, this difference dropped to 2.2-fold for 20:4, the only FFA that showed a significantly higher value between robust versus weak interictal activity. In contrast, accumulation of DAG during early and late seizures was observed only when adjacent interictal activity was high. These results indicate that the cortical accumulation of FFA and DAG during ictal periods of similar intensity and duration depends upon the electrocortical activity during adjacent interictal periods.

Differences in the acyl composition of the platelet-activating factor (PAF) precursor and other choline phosphoglycerides of the rabbit retinal rod outer segments and neural retina

Choline phosphoglycerides comprise almost half of vertebrate retinal phospholipids. This lipid pool contains the precursor of the potent lipid mediator, platelet-activating factor. The acyl composition and distribution of the different subclasses of the choline phosphoglycerides (alkylacyl-[or the precursor of platelet-activating factor], alkenylacyl-[or choline plasmalogen] and diacyl-glycero-3-phosphocholine) were studied in intact rabbit retina, neural retina and rod outer segments. Choline phosphoglycerides were isolated by high performance liquid chromatography and derivatized by acetylation after phospholipase C treatment. The derivatives were purified by high performance liquid chromatography and subjected to methanolysis. Fatty acids were analyzed by capillary gas liquid chromatography. In the intact retina and in the neural retina, the alkylacyl-glycero-3-phosphocholine and alkenylacyl-glycero-3-phosphocholine comprise 1.2% and 1.5%, respectively, of the total choline phosphoglycerides, whereas the rod outer segments contain twice the proportion of the precursor of platelet-activating factor and no detectable plasmalogens. On a mole percent basis, arachidonic acid was highest in the neural retinal alkenylacyl-glycero-3-phosphocholine (27%), 18% in the alkylacyl-glycero-3-phosphocholine and only 5% in the diacyl-glycero-3-phosphocholine. However, alkylacyl-glycero-3-phosphocholine from rod outer segments was enriched in docosapentaenoic acid (18%) while arachidonic acid was in the 3-4% range. Our results suggest that, in the neural retina, alkyl-arachidonoyl-glycero-3-phosphocholine is a source of both platelet-activating factor and of arachidonic acid which may be a substrate for both prostaglandins and lipoxygenase metabolites during an inflammatory episode and may contribute to the retinal pathology.

Docosahexaenoic acid is taken up by the inner segment of frog photoreceptors leading to an active synthesis of docosahexaenoyl-inositol lipids: similarities in metabolism in vivo and in vitro

Retinal uptake and metabolism of docosahexaenoic acid (DHA) was studied in vivo in frogs 1, 2, and 6 hours after dorsal lymph sac injections of [3H]-DHA (50 microCi/g). Light microscope autoradiography and biochemical techniques were used to compare the profiles of cellular uptake and lipid labeling with those obtained from 6 hour [3H]-DHA retinal incubations (final DHA concentration, 0.11 and 25 microM). Light microscope autoradiography demonstrated that rod photoreceptor ellipsoids and synaptic terminals preferentially labeled both in vivo and in vitro conditions. Also, the cytoplasm and oil droplets of retinal pigment epithelial cells became very heavily labeled after 6 hours of in vivo labeling. Phosphatidic acid showed the highest labeling in one hour, while other phospholipids accumulated label throughout the 6 hours. At that time point, most label was recovered in phosphatidyl-ethanolamine (37%), phosphatidylcholine (27%), and phosphatidylinositol (16%), the latter displaying 1.6-fold higher labeling than phosphatidylserine. The profile of labeled lipids was similar to that obtained in vitro when the concentration of DHA was in the nanomolar range. Our results suggest that de novo lipid synthesis is a major route for esterification of [3H]-DHA into retinal lipids, giving rise to an early and rapid labeling of DHA-phosphatidylinositol, both in vivo and in vitro, when DHA is present at low concentrations. Furthermore, the profile of labeled retinal cells under in vivo conditions closely resembles in vitro DHA labeling.

Coupling among energy failure, loss of ion homeostasis, and phospholipase A2 and C activation during ischemia

The objective of the present experiments was to correlate changes in cellular energy metabolism, dissipative ion fluxes, and lipolysis during the first 90 s of ischemia and, hence, to establish whether phospholipase A2 or phospholipase C is responsible for the early accumulation of phospholipid hydrolysis products. Ischemia was induced for 15-90 s in rats, extracellular K+ (K+e) was recorded, and neocortex was frozen in situ for measurements of labile tissue metabolites, free fatty acids, and diacylglycerides. Ischemia of 15- and 30-s duration gave rise to a decrease in phosphocreatine concentration and a decline in the ATP/free ADP ratio. Although these changes were accompanied by an activation of K+ conductances, there were no changes in free fatty acids until after 60 s, when free arachidonic acid accumulated. An increase in other free fatty acids and in total diacylglceride content did not occur until after anoxic depolarization. The results demonstrate that the early functional changes, such as activation of K+ conductances, are unrelated to changes in lipids or lipid mediators. They furthermore suggest that the initial lipolysis occurs via both phospholipase A2 and phospholipase C, which are activated when membrane depolarization leads to influx of calcium into cells.

Free fatty acid and diacylglycerol accumulation in the rat brain during recurrent seizures is related to cortical oxygenation

Cerebral blood flow and oxygenation increase during the early seizures of a series, but the increase in cerebral blood flow attenuates during late seizures, sometimes resulting in decreased cortical oxygenation. Cortical free fatty acids (FFA) and diacylglycerols also increase during early seizures and the increase attenuates during late seizures. We analyzed the correlation between lipid accumulation and cortical O2 during periodic pentylenetetrazol-induced seizures. During early seizures, both FFA and diacylglycerols increased in the cerebral cortex, particularly arachidonate (20:4) and stearate (18:0). Changes in lipids were different during late seizures, depending on cortical O2 levels. An increase in cortical O2 during late seizures was associated with lower FFA levels compared with early seizures, and FFA levels recovered to basal levels during interictal periods. A decline in cortical O2 was associated with a further increase in FFA, which remained elevated during interictal periods. Our results indicate that periseizure lipid accumulation is related to cortical oxygenation.

Decreased electroconvulsive shock-induced diacylglycerols and free fatty acid accumulation in the rat brain by Ginkgo biloba extract (EGb 761): selective effect in hippocampus as compared with cerebral cortex

The effect of Ginkgo biloba extract (EGb 761) treatment (100 mg/kg/day, per os, for 14 days) on electroconvulsive shock (ECS)-induced accumulation of free fatty acids (FFA) and diacylglycerols (DAG) was analyzed in rat cerebral cortex and hippocampus. EGb 761 reduced the FFA pool size by 33% and increased the DAG pool by 36% in the hippocampus. These endogenous lipids were unaffected in cerebral cortex. During the tonic seizure (10 s after ECS) the fast accumulation of FFA, mainly 20:4, was similar in sham- and EGb 761-treated rats, in both the cerebral cortex and hippocampus. However, further accumulation of free 18:0 and 20:4, observed in the hippocampus of sham-treated rats during clonic seizures (30 s to 2 min after ECS), did not occur in EGb 761-treated animals. The rise in DAG content triggered in the cortex and hippocampus by ECS was delayed by EGb 761 treatment from 10 s to 1 min, when values similar to those in sham animals were attained. Moreover, in the hippocampus the size of the total DAG pool was decreased by 19% during the tonic seizure. At later times, DAG content showed a faster decrease in EGb 761-treated rats. By 2 min levels of all DAG acyl groups decreased to values significantly lower than in sham animals in both cortex and hippocampus. This study shows that EGb 761 treatment affects, with high selectivity, lipid metabolism and lipid-derived second messenger release and removal in the hippocampus, while affecting to a lesser extent the cerebral cortex.

The platelet-activating factor precursor of the injured cornea is selectively implicated in arachidonate and eicosanoid release

The purpose of this study was to isolate the platelet-activating factor (PAF) precursor and other choline phosphoglycerides (GPC) i.e. the alkenylacyl and diacyl lipids from the rabbit cornea, to analyze their fatty acid content and to determine which pool was the most susceptible to arachidonate depletion when activated corneal tissue released arachidonic acid (AA) and metabolites. Rabbit iridal GPC was also analyzed for comparative purposes. The fatty acid methyl esters of the GPC components extracted from the rabbit cornea and iris-ciliary body, isolated by high performance liquid chromatography (HPLC), were determined by capillary gas liquid chromatography. Rabbit corneas were labelled in vivo by intracameral injection of 3H-AA (1 microCi, specific activity = 218 Ci/mmol) and cryogenically injured 18 h later. Corneas were incubated in vitro and the AA and eicosanoids released into the medium were extracted and separated by HPLC. The GPC was extracted from the tissues and the labeling of the three GPC constituents was quantified by liquid scintillation counting. The corneal and iridal PAF precursor represented 4.1 +/- 0.2% and 2.9 +/- 0.2% respectively of total GPC in those tissues. On a mole basis, the alkyl arachidonoyl species constituted 12.7 +/- 0.7% of the corneal and 38 +/- 0.6% of the iridal PAF precursors respectively. The release of AA and prostaglandins by the cornea was linear until 15 min; whereas 12-HETE levels continuously increased until 60 min. All GPC components lost label but 1-O-alkyl-2-arachidonoyl was the most affected, with its labeled content 50% less than the non-injured control.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipid composition of the vacuolar membrane of Acer pseudoplatanus cultured cells

Tonoplast was prepared by osmotic lysis of a pure vacuolar fraction isolated from protoplasts derived from Acer pseudoplatanus cultured cells. After their extraction, neutral and polar lipids were separated by a thin layer chromatography. Phospholipids, glycolipids and neutral lipids represented 44.5%, 39.1% and 16.4% of total lipids, respectively. Sterols (glycosylated plus non-glycosylated forms) constituted 30.8% of total lipids; 75% of sterols were glycosylated. The most prominent lipids were phosphatidylethanolamine (20.8%), phosphatidylcholine (13.5%), ceramide monohexoside (12.8%), steryl glycoside (12.2%) and acylated steryl glycoside (10.9%). Glucose was the only sugar released by acid hydrolysis of these three later compounds. The major neutral lipids were free sterols, triacylglycerols and steryl esters. The phospholipid composition was characterised by a high content of phosphatidylethanolamine (50% more than phosphatidylcholine). The fatty acid composition of phospholipids revealed two major components: palmitic and linoleic acids; they accounted together for 60 to 80% of fatty acids. When tonoplast was incubated at pH 5.5 with 5 mM Ca2+, the free fatty acid content (12% of neutral lipids) increased by 10% and lysophospholipids were detected. This indicated the presence of a calcium-dependent phospholipase A2 associated with the tonoplast.

Changing fatty acid content of growth cone lipids prior to synaptogenesis

The developing mouse was used to assess biochemical changes in membrane lipids during the period when nerve growth cones become synapses. Growth cone particles and synaptosomes were simultaneously obtained from common brain homogenates. Incorporation of the essential fatty acid, docosahexaenoic acid (22:6 omega-3), was correlated with the developmental changes in endogenous fatty acid content of growth cones and synaptosomes. Analysis of endogenous lipid content indicated that, at all ages studied, the growth cones contained more arachidonoyl acyl chains (20:4 omega-6) than did synaptosomes. Before the onset of synaptogenesis, levels of arachidonoyl chains increased and levels of 22:6, oleoyl and linoleoyl chains decreased in synaptosomes. Although stearoyl and palmitoyl (16:0) remained stable in synaptosomes, 16:0 decreased in growth cones. With the exception of 16:0 and 20:4, endogenous fatty acyl content of growth cones and synaptosomes became similar by postnatal day 10, which coincides with the onset of synaptogenesis. When 5-day-old mouse pups were injected intraperitoneally with [3H]22:6, the incorporation into growth cone and synaptosome phospholipids was greatest in phosphatidylethanolamine, followed by phosphatidylserine and phosphatidylcholine. Nominal labeling was present in phosphatidic acid and phosphatidylinositol. Labeling in neutral lipids was less than that of phospholipids, with triacylglycerol incorporating most of the neutral lipid label, followed by diacylglycerol and free 22:6. Only the growth cone fraction contained detectable amounts of 22:6-labeled cholesterol esters. The distribution of 22:6 label in plasma 72 h after injection indicated that approximately 60% of the label was in phospholipids with approximately 40% in neutral lipids and less than 5% in free fatty acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Retinal pigment epithelial cells play a central role in the conservation of docosahexaenoic acid by photoreceptor cells after shedding and phagocytosis

The involvement of retinal pigment epithelial (RPE) cells in the recycling of docosahexaenoic acid (DHA), from phagocytized disc membranes back to the retina, was studied in frogs subsequent to injection of [3H]DHA via the dorsal lymph sac. Rod outer segments (ROS) gradually accumulated [3H]DHA as a dense, heavily labeled region that arrived at the distal tips by 28 days post-injection. Autoradiographic analysis at the time of maximal shedding and phagocytosis (1-2 hr after the onset of light) showed diffusely (before 28 days) and heavily (after 28 days) labeled phagosomes in RPE cells. Biochemical analysis of the [3H]DHA-containing lipids of discs that contribute to the labeling of RPE cells after phagocytosis was also performed. Between 27 and 34 days, when 12% of retinal [3H]DHA-lipids present in disc membranes are phagocytized by RPE cells, total retinal labeling remained unchanged. Taken together, these data suggest that the [3H]DHA of the densely labeled region of the ROS was recycled back to the photoreceptor cells only after it had reached the RPE cells following 28 days post-injection. We conclude that, following daily phagocytosis of ROS tips, RPE cells play a central role in the conservation and redelivery of ROS-derived DHA back to photoreceptor cells through the interphotoreceptor matrix.

Preferential uptake and metabolism of docosahexaenoic acid in membrane phospholipids from rod and cone photoreceptor cells of human and monkey retinas

The uptake, metabolism, and cellular distribution of [3H]docosahexaenoic acid (DHA) in human and monkey retinas were studied with biochemical and autoradiographic techniques. In specimens from two human retina biopsies, incubated for 4 hr or 6 hr with [3H]docosahexaenoic acid (110 nM), 80% of the esterified [3H]fatty acid was recovered in phospholipids and the remainder in triacylglycerols and diacylglycerols. The distribution of [3H]DHA in individual phospholipids (PL) was similar in both retinas, with phosphatidylcholine (PC) and phosphatidylethanolamine (PE) accounting for most of the label. A similar labeling profile was observed in glycerolipids from monkey retina, and after 1 hr of incubation, high labeling of phosphatidic acid (PA, 11%) and phosphatidylinositol (PI, 20%) was observed. In both human and monkey retinas, a preferential uptake of [3H]DHA by photoreceptor cells was revealed by autoradiography. Cone photoreceptors showed a slightly higher density of silver grains in their inner segments than did rod photoreceptors. Photoreceptors accounted for 59% and 79% of the total [3H]DHA taken up by the human and monkey retinas, respectively, the remainder being distributed throughout the neural retina. In conclusion, this study shows for the first time that in human and monkey retinas, DHA is taken up with a high degree of selectivity by photoreceptor cells, and then becomes esterified mainly into phospholipids that will be subsequently utilized for the synthesis of new disc membranes.