An esterification protocol for cis-parinaric acid-determined lipid peroxidation in immune cells

Loss of fluorescence from cis-parinaric acid (cPnA) is a sensitive indicator of lipid peroxidation. The purpose of this study was to utilize cPnA to determine, at the level of the intact immune cell, whether enrichment of membranes with polyunsaturated fatty acids (PUFA) increased lipid peroxidation. P388D1 macrophages were labeled by addition of cPnA as an ethanolic solution. Within two minutes of addition, in the absence-of serum, cPnA rapidly intercalated into the plasma membrane. Lipid peroxidation was initiated by addition of Fe(2+)-EDTA resulting in a dose-dependent decrease in fluorescence with increased oxidant concentration. Cells previously enriched with PUFA and labeled by intercalation showed no differences in spontaneous or Fe(2+)-induced lipid peroxidation. In separate experiments, 20 microM cPnA in ethanolic solution was injected into cell culture media containing 0.1% essentially fatty acid free bovine serum albumin (BSA). Cells were resuspended and incubated for 90 min at 37 degrees C. After washing with BSA to remove cPnA which had not incorporated, 0.5% (0.1 microM) of the added cPnA was found esterified within cellular lipids. This level of cPnA provided a 100-fold increase over basal autofluorescence levels. Cells labeled in this manner also lost fluorescence in a dose-dependent manner as levels of oxidant stress increased. Cells enriched with PUFA and labeled by esterification had significantly increased rates and total amounts of lipid peroxidation. Co-incubation with alpha-tocopherol and PUFA resulted in a decrease in lipid peroxidation which was not significantly different from control cells. In conclusion, esterification of cPnA into membrane phospholipids can sensitively detect changes in lipid peroxidation induced by alteration of membrane PUFA and/or vitamin E content.

Expression of NGFI-B mRNA in a rat focal cerebral ischemia-reperfusion model

Cerebral ischemia is known to induce the expression of several immediate early genes (IEGs), including c-fos and c-jun, which subsequently regulate a number of late effector genes. In this study, we examined the expression of NGFI-B (or nur 77) mRNA in a rat focal cerebral ischemia-reperfusion model. NGFI-B is a member of the IEGs which encodes for a nuclear receptor and is rapidly induced by nerve growth factor (NGF). Northern blot analysis showed a rapid but transient enhancement of NGFI-B mRNA, a peak level for which was observed at 30 min of reperfusion following 60 min ischemic insult. At the peak level, quantitative analysis of the blot indicated a 12-fold and 4-fold increase of NGFI-B mRNA in the ischemic cortex and ipsilateral hippocampus, respectively, as compared to the sham-operated control. No apparent changes in mRNA levels were observed within contralateral sites of the cortex. Results from in situ hybridization showed that severe ischemia (60 min) resulted in a marked increase of NGFI-B mRNA throughout the entire ischemic cerebral cortex. The increase was particularly notable in the frontal, occipital, perirhinal and piriform cortical regions and in the dentate gyrus and CAI-3 regions of the ipsilateral hippocampus. A marked induction was also noted in the ipsilateral caudate putamen. Unlike the induction profile of NGFI-B mRNA, severe ischemia resulted in bilateral increases of its family gene, NGFI-A mRNA. The spatial induction profile is similar to that of NGFI-B mRNA in both hemispheres, except within the region of the contralateral dentate gyrus which showed low levels of NGFI-A mRNA. The expression pattern of NGF and BDNF mRNA, upstream genes of NGFI-B, were also examined. Interestingly the temporal and spatial expression patterns of BDNF mRNA were very similar to that of NGFI-A mRNA under the same conditions, whereas increased NGF and NGFI-B mRNA were observed only in the ipsilateral hemisphere. It is likely that multiple and/or overlapping pathways are activated subsequent to ischemic challenge which in turn are crucial for cel survival and/or functional recovery following focal cerebral ischemia.

Effects of ethanol on phosphorylation of lipids in rat synaptic plasma membranes

Synaptic plasma membranes (SPM) isolated from rat cerebral cortex contain lipid kinases for conversion of phosphatidylinositol (PI), phosphatidylinositol 4-phosphate (PIP), and diacylglycerol (DG) to PIP, phosphatidylinositol 4,5-bisphosphate (PIP2), and phosphatidic acid (PA), respectively. These anionic phospholipids are important in signal transduction mechanisms and are required for synaptic function. The effect of ethanol and other aliphatic alcohols on phosphorylation of these lipids in SPM has not been established. Incubation of SPM with [gamma-32P]ATP resulted in labeling of PIP, lyso-PIP, PIP2, and PA. Ethanol (50-200 mM) added to the incubation system showed a dose-dependent decrease in labeling of PIP2, but not PIP or PA. To a lesser extent, labeling of PIP2 was also inhibited by 1-propanol, but neither isopropanol nor 1-butanol could alter the PIP2 labeling pattern. Under similar incubation conditions, labeling of PIP and PA in SPM was not altered by ethanol, 1-propanol, iso-propanol, but 1-butanol stimulated PIP labeling with a peak at 25 mM. Addition of exogenous PIP to the incubation mixture led to an increase in labeling of PIP2, suggesting that the endogenous PIP pool in SPM is limiting for the synthesis of PIP2 in SPM. Interestingly, when SPM were incubated with exogenous PIP, addition of ethanol (50-100 mM) to this incubation mixture resulted in an increase in PIP2 labeling. Taken together, these results suggest a specific effect of ethanol on PIP kinase in SPM, and this effect seems to be dependent on the location and/or amount of PIP in the membrane.

Chronic ethanol on mRNA levels of IP3R1, IP3 3-kinase and mGluR1 in mouse Purkinje neurons

Chronic ethanol exposure is known to alter the polyphosphoinositide (poly-PI) signaling pathway, although the exact sight of regulation is not well understood. In this study, C57B1/6J mice were given a control or an ethanol (6 g kg-1 body wt) liquid diet by gastric intubation daily for 4 weeks. Examination of levels of mRNA for type 1 inositol 1,4,5-trisphosphate receptor (IP3R1), inositol 1,4,5-trisphosphate 3-kinase (IP3K) and metabotropic glutamate receptor 1 (mGluR1) in cerebellar Purkinje neurons by in situ hybridization revealed significant decreases in cellular levels of mRNA encoding both IP3R1 and mGluR1 in the ethanol-treated group compared with controls, but levels of IP3K mRNA were not altered. These results suggest that chronic ethanol consumption selectively alters cellular mRNA in the poly-PI signaling pathway. The decrease in mRNA levels of mGluR1 and IP3R1 may be an important underlying mechanism towards explaining the alcohol-induced degenerative changes in the cerebellar Purkinje neurons.

Poly-phosphoinositide-mediated messengers in focal cerebral ischemia and reperfusion

The receptor-mediated poly-phosphoinositide (PI) signalling pathway is known to play an important role in maintaining intracellular calcium homeostasis, which in turn, is critical for mediating neuronal function. In this study, we examined the effects of focal cerebral ischemia induced in rats by temporary occlusion of the middle cerebral artery (MCA) and both common carotid arteries (CCAs) on this signal transduction pathway. Results indicate that several parts of the pathway are altered, both during the early phase of focal cerebral ischemic insult and after recirculation. Cerebral ischemia induced a decrease in levels of phosphatidylinositol 4,5-bisphosphate (PIP2) in the ischemic MCA cortex, due partly to stimulated poly-PI hydrolysis and partly to the depletion of ATP required for resynthesis of this substrate. ATP depletion during ischemia was also attributed to a sustained decrease in inositol 1,4,5-trisphosphate (IP3) levels. On the other hand, the decline in IP3 3-kinase activity after 30 min of ischemic insult was not related to ATP depletion. During reperfusion upon prolonged ischemic insult, neither IP3 level nor IP3 3-kinase activity were able to show recovery after reperfusion, despite that ATP levels recovered by 80%. In situ hybridization studies indicated a decrease in mRNA expression of IP3 receptor but not IP3 3-kinase during the initial 4 h of reperfusion after a 45 min ischemic insult. Under this same condition, insulted cortical neurons started to show morphological changes between 4 and 8 h after reperfusion and extensive cell death could be observed by 16 h. Taken together, these results demonstrated early and delayed changes in the poly-PI signalling pathway due to focal cerebral ischemia. These effects are likely to cause impairment in neuronal function and underline the process of cerebral ischemic damage.

Brain neutral lipids and phospholipids are modified by long-term feeding of beef tallow vs. corn oil diets

Previous studies examining the response of brain lipids to dietary fat modification have not quantified neutral lipids such as diacylglycerols (DG) and triacylglycerols (TG). In this study we measured the concentrations of neutral lipids and phospholipids, and their fatty acid profiles, in the cerebra of rats fed defined diets containing either beef tallow (BT) or corn oil (CO) at 12% or 37% of energy. The diets were fed to rat pups beginning at 18 d of age and continued for 31 wk. The proportion of brain linoleic acid [18:2(n-6)] in TG from CO-fed rats was two- to fourfold greater than in BT-fed rats. Although 18:2(n-6) levels were higher in serum and brain TG of rats fed CO, differences in other TG fatty acid concentrations in serum were not reflected in the brain. Rats fed CO diets had higher concentrations of 18:2(n-6) in brain phospholipids as well as neutral lipids compared with rats fed BT diets, and the differences were greater in rats fed 37% rather than 12% of energy as fat. Differences in other polyunsaturated fatty acids associated with dietary fat composition were also found among the brain phospholipids. Most notably, the concentration of docosapentaenoic acid [22:5(n-6)] in brain phospholipids was highest in rats fed diets containing the lowest concentrations of alpha-linolenic acid [18:3(n-3)]. A concentration of 0.1 mg 18:3(n-3)/g diet appeared to be adequate to prevent elevation of 22:5(n-6) in brain phospholipids. These results demonstrate that consumption of a low fat diet (12% of energy) primarily comprised of saturated fats may potentiate an 18:3(n-3) deficiency in brain of rats.

In utero hypoxic ischemia decreases the cholinergic agonist-stimulated poly-phosphoinositide turnover in the developing rat brain

Perinatal hypoxic-ischemic (HI) insult is known to cause cellular and molecular disturbances leading to functional and behavioral abnormalities during brain development. In this study, we examined the effects of an in utero HI insult on poly-phosphoinositide turnover in vivo in the cerebrum and cerebellum as well as cholinergic-stimulated turnover in cortical slices from developing rat brain. In utero HI treatment was carried out by clamping the uterine blood vessels of near-term fetuses for 5, 10 and 15 min followed by resuscitation of the newborn pups. The in vivo protocol for examining poly-PI signaling activity in 2 week-old pup brain involved intracerebral injection of [3H]inositol for 16 hr and subsequent intraperitoneal injection with lithium (8 meq/kg) for 4 hr prior to decapitation. In the control pups, lithium elicited a 2.6 fold increase in labeled inositol phosphate (IP) in the cerebrum as compared to a 1.3 fold increase in the cerebellum. In utero HI insult (5 to 15 min) resulted in a small increase in labeled IP in the cerebrum but not in the cerebellum. Carbachol stimulation of poly-PI turnover was examined in brain slices prelabeled with [3H]inositol in vivo. Incubation of the prelabeled slices with carbachol in the presence of LiCl (10 mM) resulted in a time-, dose- and age-dependent increase in labeled IP. Brain slices from 2 week-old pups that experienced in utero HI-treatment for 10 and 15 min (but not 5 min) showed a significant decrease in carbachol-stimulation of labeled IP as compared with control pups. These results indicate the effects of in utero HI on the choninergic-stimulated poly-PI signaling pathway and its implication on related functional deficits in the developing brain.

Regulation of FFA by the acyltransferase pathway in focal cerebral ischemia-reperfusion

Cerebral insult is associated with a rapid increase in free fatty acids (FFA) and arachidonic acid release has been linked to the increase in eicosanoid biosynthesis. In transient focal cerebral ischemia induced by middle cerebral artery (MCA) occlusion, there is an inverse relationship between the increase in FFA and the decrease in ATP, both during the ischemia period and at later time periods after reperfusion. In this study, the focal cerebral ischemia model was used to examine incorporation of [14C]arachidonic acid into the glycerolipids in rat MCA cortex at different reperfusion times after a 60 min ischemia. The label was injected intracerebrally into left and right MCA cortex 1 hr prior to decapitation. Labeled arachidonic acid was incorporated into phosphatidylcholine, phosphatidylethanolamine and neutral glycerides. With increasing time (4-16 hr) after a 60 min ischemia, an inhibition of labeled arachidonate uptake could be found in the right ischemic MCA cortex, whereas the distribution of radioactivity among the major phospholipids was not altered. When compared to labeled PC, there was a 3-4 fold increase in incorporation of label into phosphatidic acid and triacylglycerols (TG) in the right MCA cortex, suggesting of an increase in de novo biosynthesis of TG. In an in vitro assay system, synaptosomal membranes isolated from MCA cortex 8 and 16 hr after a 60 min ischemia showed a significant decrease in arachidonoyl transfer to lysophospholipids, due mainly to a decrease in lysophospholipid:acylCoA acyltransferase activity. Assay of phospholipase A2 activity with both syaptosomes and cytosol, however, did not show differences between left and right MCA cortex or with time after reperfusion. These results suggest that besides ATP availability, the decrease in acyltransferase activity may also contribute to the increase in FFA in cerebral ischemia-reperfusion.

Inositol trisphosphate, polyphosphoinositide turnover, and high-energy metabolites in focal cerebral ischemia and reperfusion

BACKGROUND AND PURPOSE

Although the signaling pathway involving polyphosphoinositide (poly-PI) hydrolysis and release of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] is an important mechanism for regulation of neuronal calcium homeostasis, the effect of cerebral ischemia-reperfusion on this calcium signaling pathway is not well understood. Because activity of this pathway is dependent on availability of ATP, this study is aimed at examining the poly-PI signaling pathway and high-energy metabolites in a rat stroke model.

METHODS

Focal cerebral ischemia in rats was induced by temporary occlusion of the right middle cerebral artery and both common carotid arteries. Levels of Ins(1,4,5)P3 were determined by use of the radioreceptor binding assay. Poly-PI turnover in rat cortex was assessed with an in vivo protocol involving intracerebral injection of [3H] inositol and systemic administration of lithium. High-energy metabolites (ATP, ADP, and AMP) were analyzed by high-performance liquid chromatography.

RESULTS

Ischemia induced an increase in poly-PI turnover in the right middle cerebral artery cortex, but reperfusion led to a decline in this signaling activity. However, Ins(1,4,5)P3 levels decreased during ischemia, and these levels were not restored if ischemic insults were longer than 30 minutes. ATP levels decreased to 26% of control during ischemia and recovered to 80% of control during the initial 4 hours of reperfusion; these changes were followed by a second phase of decline.

CONCLUSIONS

Results show an important relationship between ischemia-induced depletion of high-energy metabolites and poly-PI signaling activity. However, the uncoupling between Ins(1,4,5)P3 and ATP during reperfusion after severe ischemia suggests that metabolism of Ins(1,4,5)P3 is more stringently regulated than ATP.

In situ hybridization of mRNA expression for IP3 receptor and IP3-3-kinase in rat brain after transient focal cerebral ischemia

Loss of intracellular calcium homeostasis has been regarded an important factor underlying neuron cell death after cerebral ischemic insult. In the brain, a major mechanism for regulation of intracellular calcium is through the signal transduction pathway involving hydrolysis of poly-phosphoinositides and release of the second messenger, inositol 1,4,5-trisphosphate (IP3). IP3 mobilizes calcium by interacting with an intracellular receptor. Upon its release after agonist stimulation, this second messenger is catabolized by a 3-kinase and a 5-phosphatase. In this study, in situ hybridization was carried out to examine the mRNA expression of IP3, receptor (IP3R) and IP3 3-kinase (IP3K) in rat brain cortex after transient focal cerebral ischemia induced by temporary occlusion of the middle cerebral artery (MCA) and the common carotid arteries (CCAs). Results indicate a large decrease (52%) in IP3R mRNA levels in the ischemic cortex as compared to that in the contralateral side at 4 h after a 45 min ischemic insult. By 16 h, practically no IP3R mRNA could be detected in the ischemic cortex. On the other hand, IP3K mRNA levels remained unaltered until 16 h after reperfusion, during which time, expression in the infarct core decreased but that surrounding the core area increased instead. Hybridization of adjacent brain sections with probes for neuron specific enolase (NSE) and beta-actin indicated also a time-dependent decrease in mRNA levels after ischemia, but these changes were less dramatic as compared to IP3R. At 16 and 24 h after reperfusion, there was an increase in beta-actin mRNA in cortical areas outside the MCA cortex, suggesting of reactive gliosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of group II phospholipase A2 mRNA expression and release in an immortalized astrocyte cell line (DITNC) by LPS, TNF alpha, and IL-1 beta. Interactive effects

Astrocytes are immunoactive cells in brain and have been implicated in the defense mechanism in response to external injury. Previous studies using cultured glial cells indicated the ability of astrocytes to respond to bacteria endotoxin and cytokines, resulting in the release of phospholipase A2. In this study, we examined the interactive effects of lipopolysaccharides (LPS), interleukin 1 beta (IL-1 beta) and tumor necrosis factor (TNF alpha) to stimulate phospholipase A2 (PLA2) in an immortalized astrocyte cell line (DITNC) with many properties of type I astrocytes. Northern blot analysis using oligonucleotide probes derived from the cDNA encoding the rat spleen group II PLA2 indicated the ability of DITNC cells to respond to all three factors in the induction of gene expression and the release of PLA2. After an initial lag time of 2 h, PLA2 release was proportional to time, reaching a plateau by 12 h. This event occurred at a time period preceding any signs of cell death. Cycloheximide at 1.25 microM completely inhibited cytokine-induced PLA2 release. When suboptimal amounts of TNF alpha were added to the DITNC culture together with IL-1 beta or LPS, a synergistic increase in the induction of PLA2 release could be observed. On the other hand, combination of IL-1 beta and LPS resulted only in an additive increase in PLA2 release. Antibodies to IL-1 beta and TNF alpha completely neutralized the effects of these two agents on PLA2 release. However, neither antibody was able to inhibit the PLA2 release induced by LPS, suggesting that the effect of LPS was not complicated by the release of IL-1 beta or TNF alpha. Taken together, results show that the immortalized astrocyte cell line (DITNC) can be used for studies to elucidate the molecular mechanism underlying the cytokine signaling cascade and subsequent induction of PLA2 synthesis.

Free fatty acids, neutral glycerides, and phosphoglycerides in transient focal cerebral ischemia

Cerebral ischemia is known to cause an increase in levels of free fatty acids (FFAs) and diacylglycerols (DGs), although the mechanism(s) leading to these changes is not well understood. In this study, we examined FFA and DG levels along with those of other lipids in rats during and after transient focal cerebral ischemia induced by temporary occlusion of the right middle cerebral artery (MCA) and both common carotid arteries. During the duration of ischemia (15-60 min), there was a time-dependent increase (two- to 10-fold) in FFA levels in the right MCA cortex, whereas levels of DG and other lipids were not altered appreciably. FFA levels in right MCA cortex returned to near control values after reperfusion. However, following a 60-min ischemic insult, there was a second phase of FFA level increase that was evident after 16 h. The FFAs accumulated during the ischemia period were different from those after reperfusion, suggesting differences in mechanisms for their release. During the second phase of FFA release, there were increases in levels of DGs and triacylglycerols (TGs) with unusually high proportions of 20:4(n-6) and 22:6(n-3). The increases in FFA, DG, and TG levels were marked by a decrease in content of phosphoglycerides (PGs). It is interesting that the increases in levels of FFAs and neutral glycerides accounted only for 10% of the total PGs depleted. The lipid changes during this reperfusion period correlated well with the development of cortical infarct.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased inositol 1,4,5-trisphosphate accumulation correlates with an up-regulation of bradykinin receptors in Alzheimer's disease

An alteration in signal transduction systems in Alzheimer's disease (AD) would likely be of pathophysiological significance, because these processes control normal brain functions. Previously, a diminished beta-adrenergic-mediated cyclic AMP response was found in cultured fibroblasts from AD patients. Because cross-talk between the phosphoinositide and cyclic AMP pathways exists, the phosphoinositide cascade was studied under conditions that were similar to those for studying the cyclic AMP response. Cells from AD patients and age-matched controls responded to bradykinin (BK) and released inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] in a time- and dose-dependent manner. The level of Ins(1,4,5)P3 increased rapidly and transiently in response to BK, peaked at 5 s, but still remained 116-132% above the basal level by 30 s. Although the temporal patterns were similar in both groups, the Ins(1,4,5)P3 concentrations in AD fibroblasts were 73 and 89% above levels in the age-matched controls at 5 and 10 s, respectively. Prostaglandin E1 also increased Ins(1,4,5)P3 formation, but this response was not different between the two groups. Although KD (affinity) values for the BK receptor were similar in both control and AD cells, the number of BK receptors (Bmax) was significantly elevated in AD fibroblasts (186.8 +/- 0.8 fmol/mg of protein) as compared with control fibroblasts (57.2 +/- 15.3 fmol/mg of protein). These results indicate that the elevated Ins(1,4,5)P3 production in response to BK in AD fibroblasts is positively correlated with an increase in the receptor numbers.

Phosphorylation of lipids in rat primary glial cells and immortalized astrocytes (DITNC)

Phosphatidylinositol 4,5-bisphosphate, a substrate in the signal transduction pathway involving phospholipase C, is synthesized in cell membranes by phosphorylation of phosphatidylinositol (PI) and phosphatidylinositol 4-phosphate (PI-4-P). Incubation with [gamma-32P]adenosine triphosphate of membranes isolated from primary glial cells in culture and from an immortalized astrocyte cell line (DITNC) and subsequent separation of the lipids by high-performance thin-layer chromatography revealed a number of labeled lipid bands. Further analysis of the deacylated products by high-performance liquid chromatography indicated the presence of two PI-4-P bands and a band corresponding to lysoPIP (PIP, PI phosphate). The two PI-4-P bands were more prominent in the samples from astrocyte cell membranes than from synaptic plasma membranes and plasma membranes. Analysis of the fatty acid composition of PI by gas-liquid chromatography revealed that both 20:3n-9 and 20:4n-6 were present in PI of cultured cell membranes, whereas the brain membranes contained exclusively 20:4n-6. The two PI-4-P bands in these membranes can be attributed to the presence of different molecular species of PI. Assignment of the fraction corresponding to lysoPIP was consistent with the observation that an increase in label in this lipid band occurred upon incubation of DITNC cell supernatant with lysoPI (1-stearoyl PI). This suggests that endogenous lysoPI present in the cell membranes can be phosphorylated to form lysoPIP.

The cholinergic receptor-linked phosphoinositide metabolism in mouse cerebrum and cerebellum in vivo

The cholinergic receptor-linked poly-phosphoinositide hydrolysis was studied in mouse cerebrum and cerebellum after prelabeling the brain with [3H]inositol. I.p. injection of Li (8 meq/kg) to C57Bl/6J mice for 4 h resulted in 14- and five-fold increases in [3H]inositol-labeled inositol monophosphate (IP1) in cerebrum and cerebellum, respectively. The labeled inositol bisphosphate (IP2) was also increased 83 and 19% in cerebrum and cerebellum, respectively. Prior injection of atropine (100 mg/kg) resulted in inhibition of Li-induced increases in labeled IP1 by 74 and 56% in cerebrum and cerebellum, respectively. Administration of pilocarpine (20 mg/kg) to the Li-treated mice for 30 min resulted in further increases in labeled IP1 and IP2 and a concomitant decrease in labeled inositol in cerebrum but not in cerebellum. Mass measurements of IP1 and IP2 isomers by HPLC revealed that inositol 1-monophosphate (Ins(1)P), inositol 4-monophosphate (Ins(4)P) and inositol 1,4-bisphosphate (Ins(1,4)P2) were all increased by pilocarpine administration in the Li-treated mouse cerebrum. The effects of pilocarpine administration in mouse cerebrum (increases in IP1 and IP2) could be completely inhibited by preinjection of atropine. Atropine injection also decreased the levels of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]. Surprisingly, a decrease in Ins(1,4,5)P3 level was also found in non-Li-treated mice after pilocarpine administration (30 mg/kg, 10-40 min). Except for the increase (20%) in [32P]-labeled PIP in the cerebrum, Li or Li together with pilocarpine administration did not alter the levels of [3H]inositol or [32P]phosphate-labeled phosphoinositides.(ABSTRACT TRUNCATED AT 250 WORDS)

Acylation of lysophosphatidylcholine by brain membranes

Brain microsomes catalyze the acylation of lysophosphatidylcholine (lysoPtdCho) in the presence and absence of added CoA derivatives. The catalytic activity is distributed widely in various subcellular fractions from rat or bovine cerebral cortex as measured by the conversion of 1-[14C]palmitoyl-sn-glycero-3-phosphocholine to [14C]PtdCho. Analysis of this latter compound revealed that the dipalmitoyl derivative is the predominant molecular species, which is formed in this reaction by transacylation between two [14C]lysoPtdCho molecules. This lysoPtdCho: lysoPtdCho transacylation reaction was enhanced several-fold by the addition of oleoyl-CoA, which also is an effective donor of acyl groups in the acyl-CoA: lysoPtdCho acyltransferase-catalyzed reaction. Measurements of the initial velocity of the transacylation reaction were used to determine kinetic constants. Apparent Km values for lysoPtdCho in the presence and absence of oleoyl-CoA were 29 microM and 104 microM, respectively, and the corresponding maximal velocities were 0.11 and 1.06 nmol.min-1.mg-1, respectively. Oleoyl-CoA at 4 microM produced half-maximal stimulation of the transacylation reaction. CoA also stimulated the rate of conversion of [14C]lysoPtdCho to [14C]PtdCho, either in the presence or absence of oleoyl-CoA, with a half-maximal effect of CoA at 80 microM. These results may be important in understanding the regulation of PtdCho synthesis and the mechanism by which acyl group composition of this compound is controlled.

Effects of focal cerebral ischemia on expression and activity of inositol 1,4,5-trisphosphate 3-kinase in rat cortex

Results from this study clearly indicate that Ins(1,4,5)P3 3-kinase is a target enzyme of cerebral ischemia insult. This enzyme is responsible for removal of Ins(1,4,5)P3 which, in turn, plays an important role in the maintenance of intracellular Ca2+ homeostasis. Not only did a time-dependent decrease in enzyme activity occur due to the focal cerebral ischemic insult, but there was also a second phase for the decline in enzyme activity around 6 h after the insult. Examination of the mRNA for the 3-kinase in frozen brain sections suggested an increase in message at a time (around 8 h) prior to development of tissue infarct. Since the initial decline in enzyme activity during ligation correlated well with the time for development of an infarct, assay of this enzyme could be used as a biochemical marker of cerebral ischemic insult.

Fatty acids in the lipids of Drosophila heads: effects of visual mutants, carotenoid deprivation and dietary fatty acids

Lipids of Drosophila heads were extracted and separated by high-performance thin-layer chromatography. Fatty acid compositions of major phospholipids as well as of triglycerides were analyzed by gas-liquid chromatography. Proportions of the major fatty acids (14:0, 16:0, 16:1, 18:0, 18:1, 18:2, 18:3) varied depending on the lipid analyzed. Docosahexaenoic acid (22:6), common in vertebrate photoreceptors and brain, and arachidonic acid (20:4), a precursor of eicosanoids, were lacking. A comparison of the fatty acid composition of the diet vs. the head suggested that Drosophila can desaturate but may not be able to elongate fatty acid carbon chains. Fatty acid analyses were carried out after the following visual system alterations: i) the transduction mutant where no receptor potential results from a deficit in phospholipase C; ii) an allele of eyes absent; iii) the mutant outer rhabdomeres absent which lacks visual pigment and rhabdomeres in the predominant type of compound eye receptor, rhabdomeres 1 through 6; and iv) carotenoid deprivation which reduces opsin and rhabdomere size. We also evaluated aging by comparing newly-emerged vs. aged wild-type flies. Alterations in fatty acid composition based on some of these manipulations were found. Based on comparisons between flies reared on media differing in C16 and C18, there is an indication that diet readily affects tissue fatty acid composition.

Effects of acute ethanol administration on polyphosphoinositide turnover and levels of inositol 1,4,5-trisphosphate in mouse cerebrum and cerebellum

Although ethanol is known for its central depressant action, its effect on the polyphosphoinositide (poly-PI) signal transduction activity in brain has not been examined in detail. In this study, C57Bl/6J mice were injected intracerebrally with [3H]inositol, and poly-PI turnover in brain was assessed by determining the levels of labeled inositol monophosphates (IP1) accumulated after intraperitoneal injection of LiCl (6 meq/kg body weight) 4 hr before killing. Using this experimental protocol, acute ethanol administration (by gavage) resulted in time- and dose-dependent decreases in the levels of labeled IP1 in both cerebrum and cerebellum as compared with controls. The ethanol-induced decrease in labeled IP1 correlated well with the decrease in levels of inositol 1,4,5-triphosphate (as measured by the radioreceptor assay) and the increase in blood ethanol concentration. Despite a 4-fold higher accumulation of labeled IP1 in the cerebrum compared with the cerebellum, there were no major differences in the steady-state levels of inositol 1,4,5-triphosphate (based on tissue weight) in either brain region. Intraperitoneal injection of atropine (50 mg/kg) (a muscarinic cholinergic receptor antagonist) to the lithium-treated mice resulted in a 34% decrease in labeled IP1 as compared with controls. This result suggests that a substantial proportion of the signals transduced were due to activation of the muscarinic cholinergic receptor. Administration of ethanol (5 g/kg) to the atropine-treated mice resulted in a further decrease in labeled IP1 and longer sleep time as compared with those given ethanol alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism of inositol 1,4,5-trisphosphate in mouse brain due to decapitation ischemic insult: effects of acute lithium administration and temporal relationship to diacylglycerols, free fatty acids and energy metabolites

Previous studies have shown that global cerebral ischemia induced by decapitation leads to the stimulated hydrolysis of poly-phosphoinositides. In this study, the decapitation model was used to further examine the temporal events related to metabolism of Ins(1,4,5)P3 and the release of diacylglycerols (DGs) and free fatty acids (FFAs) in the mouse brain. Since lithium administration is known to inhibit inositol monophosphatase activity in brain, the effects of acute lithium injection on Ins(1,4,5)P3 metabolism were also examined. Cerebral ischemia induced by decapitation of C57 Bl/6J mice resulted in transient increases of Ins(1,4,5)P3, Ins(1,4)P2 and Ins(4)P which peaked at 35, 65 and 125 s, respectively. The level of Ins(1)P, however, was not altered. Mice administered lithium by intraperitoneal injection (8 meq/kg for 4 h) gave rise to a 40- and 4-fold increase in levels of Ins(1)P, Ins(4)P, respectively, a 20% increase in levels of Ins(1,4)P2 but no apparent changes in the levels of Ins(1,4,5)P3. Decapitation also induced an increase in the levels of DGs and FFAs. Unlike the transient appearance of Ins(1,4,5)P3, however, DG levels increased steadily for 2 min and then reached a plateau whereas the FFAs showed a lag time of 35 s prior to a biphasic increase. During the initial 2 min after decapitation, there was a preferential increase in the DG species containing 18:0 and 20:4. Lithium administration did not alter the decapitation-induced release of DG and FFA. As expected, decapitation gave rise to a rapid decrease in the levels of phosphocreatine and ATP and the decline in ATP was marked by a transient appearance of ADP and a concomitant increase in AMP.(ABSTRACT TRUNCATED AT 250 WORDS)

Signal transduction pathways coupled to a P2U receptor in neuroblastoma x glioma (NG108-15) cells

Extracellular ATP has neurotransmitter-like properties in the CNS and PNS that are mediated by a cell-surface P2 purinergic receptor. In the present study, we have extensively characterized the signal transduction pathways that are associated with activation of a P2U receptor in a cultured neuroblastoma x glioma hybrid cell line (NG108-15 cells). The addition of > or = 1 microM ATP to NG108-15 cells caused a transient increase in [Ca2+]i that was inhibited by 40% when extracellular calcium was chelated by EGTA. ATP concentrations > or = 500 microM also elicited a sustained increase in [Ca2+]i that was inhibited when extracellular calcium was chelated by EGTA. The increase in [Ca2+]i elicited by ATP occurred concomitantly with the hydrolysis of [32P]-phosphatidylinositol 4,5-bisphosphates and an increase in the level of inositol 1,4,5-trisphosphate. ATP also caused a time- and dose-dependent increase in levels of [3H]inositol monophosphates in lithium-treated cells. Separation of the inositol monophosphate isomers by ion chromatography revealed a specific increase in the level of inositol 4-monophosphate. The magnitude of the increase in [Ca2+]i elicited by ATP correlated with the concentration of the fully ionized form of ATP (ATP4-) in the medium and not with the concentration of magnesium-ATP (MgATP2-). Similar to ATP, UTP also induced polyphosphoinositide breakdown, inositol phosphate formation, and an increase in [Ca2+]i. ADP, ITP, TTP, GTP, ATP gamma S, 2-methylthio ATP, beta, gamma-imidoATP or 3'-O-(4-benzoyl)benzoylATP, but not CTP, AMP, beta, gamma-methylene ATP, or adenosine, also caused an increase in [Ca2+]i. In cells labeled with [32P]P(i) or [14C]-arachidonic acid, ATP caused a transient increase in levels of labeled phosphatidic acids, but had no effect on levels of arachidonic acid. The increase in phosphatidic acid levels elicited by ATP apparently was not due to activation of a phospholipase D because ATP did not induce the formation of phosphatidylethanol in [14C]myristic acid-labeled cells incubated in the presence of ethanol. These findings support the hypothesis that a P2 nucleotide receptor in NG108-15 cells is coupled to a signal transduction pathway involving the activation of a phospholipase C and a plasma membrane calcium channel, but not the activation of phospholipases A2 and D.

Endothelin-mediated calcium response and inositol 1,4,5-trisphosphate release in neuroblastoma-glioma hybrid cells (NG108-15): cross talk with ATP and bradykinin

Addition of endothelins (ETs) to neuroblastoma-glioma hybrid cells (NG108-15) induced increases in cytosolic free Ca2+ ([Ca2+]i) levels of labeled inositol monophosphates and inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]. The increases in [Ca2+]i elicited by the three ETs (ET-1, ET-2, and ET-3) were transient and did not show a sustained phase. Chelating extracellular Ca2+ in the medium by adding excess EGTA decreased the ET-mediated Ca2+ response by 40-50%. This result indicates that a substantial portion of the increase in [Ca2+]i was due to influx from an extracellular source. However, the increase in [Ca2+]i was not affected by verapamil or nifedipine (10(-5) M). A rank order potency of ET-1 > ET-2 > ET-3 is shown for the stimulated increase in [Ca2+]i, as well as labeled inositol phosphates, in these cells. ATP (10(-4) M) and bradykinin (10(-7) M) also induced the increases in [Ca2+]i and Ins(1,4,5)P3 in NG108-15 cells, albeit to a different extent. When compared at 10(-7) M, bradykinin elicited a five- to sixfold higher increase in the level of Ins(1,4,5)P3, but less than a twofold higher increase in [Ca2+]i than those induced by ET-1. Additive increases in both Ins(1,4,5)P3 and [Ca2+]i were observed when ET-1, ATP, and bradykinin were added to the cells in different combinations, suggesting that each receptor agonist is responsible for the hydrolysis of a pool of polyphosphoinositide within the membrane. ET-1 exhibited homologous desensitization of the Ca2+ response, but partial heterologous desensitization to the Ca2+ response elicited by ATP. On the contrary, ET-1 did not desensitize the response elicited by bradykinin, although bradykinin exhibited complete heterologous desensitization to the response elicited by ET-1. Taken together, these results illustrate that, in NG108-15 cells, a considerable amount of receptor cross talk occurs between ET and other receptors that transmit signals through the polyphosphoinositide pathway.

Effects of lysophospholipids and diacylglycerols on the transfer of arachidonic acid to phospholipids and triacylglycerols in rat brain membranes

Brain membranes catalyze the acylation of lysophospholipids and diacylglycerols (DAG) to form the respective phospholipids and triacylglycerols (TAG). These acylation reactions were examined using brain plasma membrane-enriched fractions by measuring the incorporation of [14C]arachidonic acid into TAG and individual phospholipids under a variety of conditions. In the absence of added lipid substrates, the amount of [14C]arachidonic acid incorporated into TAG in the presence of ATP, Mg2+, and CoA was approx twice the amount incorporated into phosphatidylositol (PtdIns), and more than 10 times the amount incorporated into phosphatidylcholine (PtdCho), phosphatidylethanolamine (PtdEtn) and phosphatidylserine (PtdSer). These results suggest the presence of endogenous DAG, lysoPtdIns, and the required enzymes in the membrane preparations for acylation reactions. The addition of DAG, lysoPtdCho or lysoPtdIns to the incubation system resulted in a 2-20-fold increase in the rate of incorporation of labeled arachidonic acid into TAG, PtdCho or PtdIns, respectively. LysoPtdEtn and lysoPtdSer were poor substrates for the synthesis of PtdEtn and PtdSer. On the other hand, the addition of lysoPtdSer stimulated the incorporation of [14C]arachidonic acid into TAG and into most phospholipids, especially phosphatidic acid, the synthesis of which was enhanced more than 10-fold. Exogenous lysoPtdCho and lysoPtdIns inhibited the incorporation of [14C]arachidonate into TAG in the presence of DAG, and DAG inhibited the incorporation of [14C]arachidonic acid into phospholipids in the presence of lysophospholipids. In general, [14C]palmitic acid was less effectively incorporated into lipids than arachidonic acid. These results suggest reciprocal regulatory effects of DAG and lysophospholipids on acyltransfer to phospholipids and triacylglycerol in brain membranes.