BACKGROUND
the metabolic syndrome is a clinical disorder characterized by obesity, hypertension, dyslipidemia, glucose intolerance and peripheral inflammation  <cit> , and is a risk factor for cognitive decline and mood disorders  <cit> .
in rodent models of the metabolic syndrome, behavioral abnormalities have been linked to cerebral hypoglycemia  <cit>  and increased cytokine production  <cit> , and changes in brain lipid metabolism  <cit> .
the brain is highly enriched with the polyunsaturated fatty acids , arachidonic acid  and docosahexaenoic acid   <cit> , which mostly are esterified in the stereospecifically numbered- <dig> position of membrane phospholipids.
aa and dha are essential for mediating neuroreceptor signaling, while excessive aa is released during neuroinflammation and excitotoxicity  <cit> .
stimulation of aa signaling by glutamatergic, serotonergic, cholinergic or dopaminergic neuroreceptors, among others, triggers aa release by aa-selective ca2+-dependent cytosolic phospholipase a <dig>  .
unesterified aa is a precursor of prostaglandins, thromboxanes, leukotrienes, and related compounds that have important roles in regulating the brain’s neuroinflammatory response  <cit> .
stimulation of dha release from membrane phospholipid via dha-selective calcium-independent ipla <dig> type via is thought to be neuroprotective, and shows anti-inflammatory effects based on in vitro and in vivo studies  <cit> .
disturbed brain aa and dha metabolism has been linked to a number of neurodegenerative diseases, including alzheimer’s disease and bipolar disorder  <cit> , which are more common in individuals with the metabolic syndrome  <cit> .
brain lipid metabolism is altered in the metabolic syndrome.
in a rat model of intracerebroventricular streptozotocin-induced brain insulin resistance and hypoglycemia, cerebral cortex concentrations of ethanolamine glycerophospholipid  and phosphatidylserine  were decreased, while concentrations of unesterified palmitate, stearate and aa were increased, suggesting increased pla2-mediated membrane degradation  <cit> .
brain phospholipid concentration was reported reduced in a genetic mouse model of diabetes  <cit> .
an increased hippocampal malonaldehyde concentration, a marker of pufa oxidative degradation, was reported in the hippocampus of genetically obese and hypertensive rats  <cit> .
taken together, these studies suggest an effect of the metabolic syndrome on the enzymes that regulate brain pufa metabolism, such as aa-selective cpla <dig> iva and ipla <dig> via, which prefers dha but also can release aa  <cit> .
unesterified aa can be converted to pro-inflammatory and pro-apoptotic secondary mediators, such as prostaglandin e <dig> , thromboxane b <dig>   <dig> and leukotriene b <dig> , via cyclooxygenase- <dig>  or  <dig>   <dig> and  <dig> lipoxygenase   <cit> .
these eicosanoids can cause synaptic-dendritic injury by reducing brain levels of trophic factors, such as brain-derived neurotrophic factor   <cit> .
in this regard, studies reported decreased bdnf and synaptic loss  <cit>  in association with cognitive impairment and behavioral changes, in animal models of the metabolic syndrome  <cit> .
although ipla <dig> via can regulate peripheral glucose-stimulated insulin secretion, apoptosis and mitochondrial fatty acid oxidation  <cit> , its involvement in modulating brain lipid metabolism in the metabolic syndrome is not known  <cit> .
in view of the reported changes in brain concentrations of phospholipids and pufas, and of neuronal loss in animal models of the metabolic syndrome  <cit> , we hypothesized correlated disturbances in brain cpla <dig> iva and ipla <dig> via expression, fatty acid concentrations, synaptic loss, bdnf, and pge <dig>  txb <dig> and lxb <dig> concentrations.
such changes have been reported in animal models of neuroinflammation  <cit> .
to test this hypothesis, we induced early-stage metabolic syndrome by feeding rats a high-sucrose diet for  <dig> weeks.
in this model, feeding a high-sucrose diet induces time-dependent changes in insulin-resistance and in other markers of the metabolic syndrome after  <dig> weeks  <cit> , without causing diabetic pathology, fatty liver or weight gain  <cit> , which may independently alter brain lipid metabolism  <cit> .
insulin resistance can be induced in this model without changing the fat composition of the diet, thereby eliminating confounding effects of diet on brain fatty acid composition  <cit> .
in sucrose and control diet fed rats maintained for  <dig> weeks, we examined brain 1) expression of enzymes involved in aa and dha metabolism ; 2) concentrations of pge <dig>  txb <dig> and lxb4; 3) mrna levels of glial-fibrillary acidic protein  and tumor-necrosis factor-α , because of reported changes in these inflammatory markers in animal models of the metabolic syndrome  <cit> ; 4) expression of bdnf, and of synaptophysin and drebrin as markers of synapto-dendritic injury  <cit> ; and 5) esterified fatty acid concentrations in phospholipid subclasses, as well as unesterified fatty acids and lysophosphatidylcholine , as markers of phospholipid degradation.
these measurements were performed to test whether phospholipase-mediated phospholipid breakdown occurs in this dietary rat model of the metabolic syndrome, in association with neuroinflammation and synapto-dendritic injury.
these pathways are physiologically related because cytokine-induced inflammation, if present in the metabolic syndrome, can alter the expression aa or dha-selective pla2’s and their downstream metabolites  that modulate synapto-dendritic integrity and bdnf expression .
RESULTS
weight gain and food intake
figure  <dig> shows body weight  and food intake  over the 8-week course of the study.
two-way repeated measures analysis of variance revealed a significant main effect of time on weight and food intake, both of which increased.
no significant effect of diet or interaction between diet and time was seen.
consistent with the lack of difference in body weight, weights of brain, liver, adipose tissue, heart, kidneys and testes, collected at the time of sacrifice, did not differ significantly between the two groups .
oral glucose tolerance test
rats fed the high-sucrose diet showed evidence of impaired glucose metabolism, measured by an oral glucose tolerance test at  <dig> and  <dig> weeks.
two-way repeated measures analysis of variance showed a significant main effect of diet and time on whole blood glucose concentrations at  <dig>  and  <dig> weeks .
at  <dig> and  <dig> weeks, fasting whole blood glucose concentration was similar between the two groups at baseline.
the glucose concentration was increased after an oral preload of glucose  and remained higher than baseline values by the end of the  <dig> h test.
the rise in blood glucose concentration was significantly higher for the high-sucrose compared to control rats, suggesting reduced glucose tolerance in the sucrose- group.
ß-hydroxybutyrate in whole blood
fasting ß-hydroxybutyrate concentration in whole blood, a marker of ketosis, was measured at  <dig> and  <dig> weeks, before starting the oral glucose tolerance test .
there was a significant effect of time on fasting ß-hydroxybutyrate concentration, but no effect of treatment or an interaction between time and diet.
ß-hydroxybutyrate concentrations were significantly reduced for both dietary groups at  <dig> weeks compared to  <dig> weeks .
values are means ± sd  1n= <dig> due to insufficient sample.
1n= <dig> due to insufficient sample.
data were analyzed by two-way repeated measures anova, followed by a one-way anova and bonferroni’s post-hoc test comparing high-sucrose versus controls at  <dig> and  <dig> weeks.
**p <  <dig> ; ***p <  <dig>  indicates significant difference compared to 8-week control mean.
plasma insulin, glucose and triglyceride concentrations
rats on the high-sucrose diet showed insulin resistance and hypertriglyceridemia at  <dig> but not  <dig> weeks .
there was a significant interaction between time and diet  for fasting plasma, insulin, and triglyceride concentrations, and the homeostasis model assessment  insulin-resistance index, calculated as previously described  <cit> .
there was a significant main effect of diet on plasma glucose and triglyceride concentrations, and on the homa index.
time was a significant factor affecting glucose, insulin and triglyceride concentrations, and the homa index.
compared to controls, rats fed the high-sucrose diet had significantly higher plasma concentrations of glucose and triglycerides and homa index at  <dig> weeks.
cpla <dig> mrna and protein
mrna and protein levels of brain cpla <dig> iva did not differ significantly between rats fed the high sucrose and the control diet for  <dig> weeks .
the protein level of phosphorylated-cpla <dig> , which represents the active form of cpla <dig> <cit> , was increased significantly in the high-sucrose group compared to the control group .
consistent with the increase, in phosphorylated-cpla <dig> activity of cpla <dig> was significantly increased in the high-sucrose group .
ipla <dig> and spla <dig> mrna, protein and activity
ipla <dig> via and spla <dig> iia mrna and protein did not differ significantly between rats fed the high sucrose and the control diet for  <dig> weeks .
the activity of ipla <dig> was significantly increased in the high-sucrose group , whereas spla <dig> activity did not differ significantly between the groups .
pge <dig>  txb <dig> and ltb <dig> concentrations
there was no significant difference in pge <dig>  ltb <dig> or txb <dig> concentration between the two groups .
gfap, tnf-α, cox and lox mrna
there was no significant change in gfap or tnf-α mrna .
mrna levels of cox- <dig> and cox- <dig> also were not affected by the high-sucrose diet , nor was 5- or 15-lox mrna changed significantly.
brain 12-lox mrna was increased significantly .
mrna and protein levels of bdnf and synaptic markers
compared with control diet, the high-sucrose diet decreased significantly mean protein and mrna levels of bdnf .
mrna and protein levels of the pre-synaptic marker synaptophysin did not differ significantly between the groups .
there was a significant decrease in mrna of the post-synaptic dendritic spine marker  <cit> , drebrin , but no significant change in its protein level .
brain fatty acid concentrations
there were few significant differences in brain esterified fatty concentrations : a 12-16% increase in aa  and adrenate  in etngpl, and a 29% increase in dihomo-γ-linolenic acid  in lysopc in rats on the high-sucrose compared to control diet .
for unesterified fatty acids, one sample from the high-sucrose group was excluded from the analysis because its unesterified aa concentration was 3-fold higher than the mean, which suggests ischemia caused by incomplete microwave-fixation  <cit> .
the unesterified aa concentration was significantly increased  in the high-sucrose diet group, whereas the dha concentration did not differ significantly from control .
other unesterified fatty acid concentrations also did not differ between the groups .
discussion
rats fed the high-sucrose diet  for  <dig> weeks did not show obesity or increased food intake, but developed hypertriglyceridemia and insulin resistance, two components of the metabolic syndrome, as reported  <cit> .
at  <dig> weeks, some brain enzymatic markers of aa and dha metabolism were increased significantly in the high sucrose compared with control diet group  as was the esterified aa concentration in etngpl and unesterified aa concentration.
bdnf mrna and protein and drebrin mrna were reduced, but synaptophysin mrna and protein were not altered.
feeding the high-sucrose diet for  <dig> weeks did not change pge <dig>  txb <dig> or ltb <dig> concentration significantly.
because the 8-week high-sucrose feeding paradigm represents early-stage metabolic syndrome in the absence of pathological diabetes or obesity  <cit> , these findings demonstrate changes in brain pufa metabolizing enzymes and composition in association with reduced bdnf and drebrin mrna at an early disease stage.
the upregulation of brain cpla <dig> and ipla <dig> enzyme activities  in the high-sucrose fed rats suggests an increase in brain aa and dha metabolism.
in this regard, disturbed saturated brain fatty acid metabolism has been reported in humans and rats with the metabolic syndrome  <cit> .
a positron emission tomography study demonstrated increased brain uptake of 11c]palmitate and 18f]fluoro-6-thia-heptadecanoic acid in patients with the metabolic syndrome  <cit> .
hypothalamic concentrations of long-chain saturated acyl-coas were increased in a high-fat diet animal model of the metabolic syndrome, also indicating increased metabolism of long-chain saturated fatty acids  <cit> .
taken together, the results suggest non-specific upregulation in brain fatty acid metabolism, including pufas, associated with the metabolic syndrome.
upregulated aa or dha metabolism could be directly confirmed in this animal model, using quantitative autoradiography to image fatty acid uptake following radiotracer injection, or can be examined in humans using positron emission tomography  <cit> .
the released fatty acids may be alternative energy substrates to glucose for brain metabolism, due to cerebral hypoglycemia caused by insulin-resistance.
this is consistent with evidence of increased brain activity of carnitine palmitoyltransferase  in an animal model of the metabolic syndrome  <cit> .
14c-palmitate conversion to 14c-co <dig> also was increased in mitochondrial brain extracts of diabetic  mice  <cit> .
brain cpla <dig> activity and phospho-cpla <dig> protein, a marker of activated cpla <dig> <cit> , were increased in the high-sucrose fed rats in the absence of changes in cpla <dig> mrna or protein, suggesting post-translational modification and upregulated brain aa metabolism, consistent with the increased unesterified aa concentration .
increased activation of cpla <dig> may reflect excitotoxicity associated with increased influx of extracellular calcium into the cell via ionotropic glutamatergic receptors  <cit> .
since cpla <dig> also is functionally coupled via g-proteins to dopaminergic, serotonergic and muscarinic neuroreceptors  <cit> , an increase in its activity suggests disturbed g-protein neuroreceptor signaling in the metabolic syndrome  <cit> .
cytokine receptor activation may also initiate cpla <dig> activation  <cit> , although our findings do not suggest an increase in cytokine expression in rats fed the high-sucrose diet.
ipla <dig> is insensitive to extracellular calcium influx into the neuron  <cit> , but can be activated by intracellular calcium  released from the endoplasmic reticulum by the calcium-releasing ryanodine receptor  <cit> .
mobilization of intracellular calcium stores can be mediated by increased intracellular unesterified aa levels, which was reported to activate the ryanodine receptor in vitro <cit> .
this is in agreement with the finding that the unesterified aa concentration was increased in the high-sucrose diet rats .
likely, this increase in aa concentration occurred intracellularly, since spla <dig>  which releases aa extracellularly, was not changed significantly .
concentrations of pro-inflammatory eicosanoids  did not differ between the groups .
it is possible, however, that changes in eicosanoids or cytokines  <cit>  occurred in specific brain regions such as the hippocampus, as reported in genetically diabetic mice, or that longer administration of the high-sucrose diet sufficient to initiate diabetes would increase whole brain cytokine levels  <cit> .
however, consistent with the lack of significant changes in the three eicosanoids, we did not find significant changes in mrna levels for cox- <dig>  cox- <dig>  5- or 15-lox in the high-sucrose fed rats, nor in tnf-α or gfap mrna, suggesting the absence of neuroinflammation, since transcription of these molecular markers occurs within transcriptional circuits related to neuroinflammation  <cit> .
whole brain bdnf mrna and protein levels were reduced in the high-sucrose group , in agreement with previous studies that showed reduced bdnf levels in animal models of the metabolic syndrome with behavioral impairment  <cit> .
reduced bdnf expression was not mediated by pro-inflammatory eicosanoids, which were not changed.
one possibility is that the increased unesterified aa concentration in the high-sucrose animals decreased bdnf and induced apoptosis, as reported in cultured spinal cord neurons  <cit> .
reduced bdnf expression in the sucrose-fed rats may have promoted dendritic injury, which was indirectly suggested by the reduction in drebrin mrna , or have altered the cellular dynamics and structural organization of dendritic spines in the absence of changes in drebrin protein.
changes in dendritic morphology and dynamics could be the topic of future studies.
additionally, more severe changes in synaptic structure are likely to occur with prolonged exposure to the high-sucrose diet, since the 8-week feeding paradigm causes only early-stage metabolic syndrome without obesity, diabetes or liver damage  <cit> .
contrary to reports using other models involving central insulin resistance  <cit> , we did not find evidence of phospholipid degradation in the brain, since phospholipid mass, derived by the summation of total fatty acids within each phospholipid class, did not differ between the dietary groups .
also, lysopc, a marker of phospholipid breakdown, was not changed .
the changes in phospholipid fatty acid concentrations were relatively minor, and were significant only for a few n- <dig> pufas in etngpl  and in lysopc .
CONCLUSIONS
in summary, brain enzymatic markers of aa and dha metabolism were increased in a rat model of early-stage metabolic syndrome, in association with reduced bdnf mrna and protein, and drebrin mrna.
increases in cpla <dig> and ipla <dig> activities support the notion of phospholipase-mediated neurodegeneration  <cit> .
the decreases in bdnf and drebrin suggest increased susceptibility to synapto-dendritic injury.
in the future, an upregulation in brain aa and dha metabolism associated with the metabolic syndrome might be imaged in humans with positron-emitting tomography using radiolabeled aa or dha  <cit> , as biomarkers of disease progression  <cit> .
therapeutic strategies aimed at downregulating brain pufa metabolism, such as the administration of carnitine palmitoyltransferase inhibitors  <cit>  or pla <dig> inhibitors , might be effective in slowing the progression of brain lipid abnormalities identified in this study, the associated changes in synaptic loss and possibly, cognitive dysfunction in the metabolic syndrome.

 the metabolic syndrome is a clinical disorder characterized by obesity, hypertension, dyslipidemia, glucose intolerance and peripheral inflammation, and is a risk factor for cognitive decline and mood disorders. in rodent models of the metabolic syndrome, behavioral abnormalities have been linked to cerebral hypoglycemia and increased cytokine production, and changes in brain lipid metabolism. the brain is highly enriched with the polyunsaturated fatty acids, arachidonic acid and docosahexaenoic acid, which mostly are esterified in the stereospecifically numbered- position of membrane phospholipids. aa and dha are essential for mediating neuroreceptor signaling, while excessive aa is released during neuroinflammation and excitotoxicity. stimulation of aa signaling by glutamatergic, serotonergic, cholinergic or dopaminergic neuroreceptors, among others, triggers aa release by aa-selective ca2+-dependent cytosolic phospholipase a. unesterified aa is a precursor of prostaglandins, thromboxanes, leukotrienes, and related compounds that have important roles in regulating the brain’s neuroinflammatory response. stimulation of dha release from membrane phospholipid via dha-selective calcium-independent ipla type via is thought to be neuroprotective, and shows anti-inflammatory effects based on in vitro and in vivo studies. disturbed brain aa and dha metabolism has been linked to a number of neurodegenerative diseases, including alzheimer’s disease and bipolar disorder, which are more common in individuals with the metabolic syndrome. brain lipid metabolism is altered in the metabolic syndrome. in a rat model of intracerebroventricular streptozotocin-induced brain insulin resistance and hypoglycemia, cerebral cortex concentrations of ethanolamine glycerophospholipid and phosphatidylserine were decreased, while concentrations of unesterified palmitate, stearate and aa were increased, suggesting increased pla2-mediated membrane degradation. brain phospholipid concentration was reported reduced in a genetic mouse model of diabetes. an increased hippocampal malonaldehyde concentration, a marker of pufa oxidative degradation, was reported in the hippocampus of genetically obese and hypertensive rats. taken together, these studies suggest an effect of the metabolic syndrome on the enzymes that regulate brain pufa metabolism, such as aa-selective cpla iva and ipla via, which prefers dha but also can release aa. unesterified aa can be converted to pro-inflammatory and pro-apoptotic secondary mediators, such as prostaglandin e, thromboxane b and leukotriene b, via cyclooxygenase- or and lipoxygenase. these eicosanoids can cause synaptic-dendritic injury by reducing brain levels of trophic factors, such as brain-derived neurotrophic factor. in this regard, studies reported decreased bdnf and synaptic loss in association with cognitive impairment and behavioral changes, in animal models of the metabolic syndrome. although ipla via can regulate peripheral glucose-stimulated insulin secretion, apoptosis and mitochondrial fatty acid oxidation, its involvement in modulating brain lipid metabolism in the metabolic syndrome is not known. in view of the reported changes in brain concentrations of phospholipids and pufas, and of neuronal loss in animal models of the metabolic syndrome, we hypothesized correlated disturbances in brain cpla iva and ipla via expression, fatty acid concentrations, synaptic loss, bdnf, and pge txb and lxb concentrations. such changes have been reported in animal models of neuroinflammation. to test this hypothesis, we induced early-stage metabolic syndrome by feeding rats a high-sucrose diet for weeks. in this model, feeding a high-sucrose diet induces time-dependent changes in insulin-resistance and in other markers of the metabolic syndrome after weeks, without causing diabetic pathology, fatty liver or weight gain, which may independently alter brain lipid metabolism. insulin resistance can be induced in this model without changing the fat composition of the diet, thereby eliminating confounding effects of diet on brain fatty acid composition. in sucrose and control diet fed rats maintained for weeks, we examined brain 1) expression of enzymes involved in aa and dha metabolism; 2) concentrations of pge txb and lxb4; 3) mrna levels of glial-fibrillary acidic protein and tumor-necrosis factor-α, because of reported changes in these inflammatory markers in animal models of the metabolic syndrome; 4) expression of bdnf, and of synaptophysin and drebrin as markers of synapto-dendritic injury; and 5) esterified fatty acid concentrations in phospholipid subclasses, as well as unesterified fatty acids and lysophosphatidylcholine, as markers of phospholipid degradation. these measurements were performed to test whether phospholipase-mediated phospholipid breakdown occurs in this dietary rat model of the metabolic syndrome, in association with neuroinflammation and synapto-dendritic injury. these pathways are physiologically related because cytokine-induced inflammation, if present in the metabolic syndrome, can alter the expression aa or dha-selective pla2’s and their downstream metabolites that modulate synapto-dendritic integrity and bdnf expression.  weight gain and food intake figure  shows body weight and food intake over the 8-week course of the study. two-way repeated measures analysis of variance revealed a significant main effect of time on weight and food intake, both of which increased. no significant effect of diet or interaction between diet and time was seen. consistent with the lack of difference in body weight, weights of brain, liver, adipose tissue, heart, kidneys and testes, collected at the time of sacrifice, did not differ significantly between the two groups. oral glucose tolerance test rats fed the high-sucrose diet showed evidence of impaired glucose metabolism, measured by an oral glucose tolerance test at and weeks. two-way repeated measures analysis of variance showed a significant main effect of diet and time on whole blood glucose concentrations at and weeks. at and weeks, fasting whole blood glucose concentration was similar between the two groups at baseline. the glucose concentration was increased after an oral preload of glucose and remained higher than baseline values by the end of the h test. the rise in blood glucose concentration was significantly higher for the high-sucrose compared to control rats, suggesting reduced glucose tolerance in the sucrose- group. ß-hydroxybutyrate in whole blood fasting ß-hydroxybutyrate concentration in whole blood, a marker of ketosis, was measured at and weeks, before starting the oral glucose tolerance test. there was a significant effect of time on fasting ß-hydroxybutyrate concentration, but no effect of treatment or an interaction between time and diet. ß-hydroxybutyrate concentrations were significantly reduced for both dietary groups at weeks compared to weeks. values are means ± sd 1n= due to insufficient sample. 1n= due to insufficient sample. data were analyzed by two-way repeated measures anova, followed by a one-way anova and bonferroni’s post-hoc test comparing high-sucrose versus controls at and weeks. **p <; ***p < indicates significant difference compared to 8-week control mean. plasma insulin, glucose and triglyceride concentrations rats on the high-sucrose diet showed insulin resistance and hypertriglyceridemia at but not weeks. there was a significant interaction between time and diet for fasting plasma, insulin, and triglyceride concentrations, and the homeostasis model assessment insulin-resistance index, calculated as previously described. there was a significant main effect of diet on plasma glucose and triglyceride concentrations, and on the homa index. time was a significant factor affecting glucose, insulin and triglyceride concentrations, and the homa index. compared to controls, rats fed the high-sucrose diet had significantly higher plasma concentrations of glucose and triglycerides and homa index at weeks. cpla mrna and protein mrna and protein levels of brain cpla iva did not differ significantly between rats fed the high sucrose and the control diet for weeks. the protein level of phosphorylated-cpla, which represents the active form of cpla, was increased significantly in the high-sucrose group compared to the control group. consistent with the increase, in phosphorylated-cpla activity of cpla was significantly increased in the high-sucrose group. ipla and spla mrna, protein and activity ipla via and spla iia mrna and protein did not differ significantly between rats fed the high sucrose and the control diet for weeks. the activity of ipla was significantly increased in the high-sucrose group, whereas spla activity did not differ significantly between the groups. pge txb and ltb concentrations there was no significant difference in pge ltb or txb concentration between the two groups. gfap, tnf-α, cox and lox mrna there was no significant change in gfap or tnf-α mrna. mrna levels of cox- and cox- also were not affected by the high-sucrose diet, nor was 5- or 15-lox mrna changed significantly. brain 12-lox mrna was increased significantly. mrna and protein levels of bdnf and synaptic markers compared with control diet, the high-sucrose diet decreased significantly mean protein and mrna levels of bdnf. mrna and protein levels of the pre-synaptic marker synaptophysin did not differ significantly between the groups. there was a significant decrease in mrna of the post-synaptic dendritic spine marker, drebrin, but no significant change in its protein level. brain fatty acid concentrations there were few significant differences in brain esterified fatty concentrations: a 12-16% increase in aa and adrenate in etngpl, and a 29% increase in dihomo-γ-linolenic acid in lysopc in rats on the high-sucrose compared to control diet. for unesterified fatty acids, one sample from the high-sucrose group was excluded from the analysis because its unesterified aa concentration was 3-fold higher than the mean, which suggests ischemia caused by incomplete microwave-fixation. the unesterified aa concentration was significantly increased in the high-sucrose diet group, whereas the dha concentration did not differ significantly from control. other unesterified fatty acid concentrations also did not differ between the groups. discussion rats fed the high-sucrose diet for weeks did not show obesity or increased food intake, but developed hypertriglyceridemia and insulin resistance, two components of the metabolic syndrome, as reported. at weeks, some brain enzymatic markers of aa and dha metabolism were increased significantly in the high sucrose compared with control diet group as was the esterified aa concentration in etngpl and unesterified aa concentration. bdnf mrna and protein and drebrin mrna were reduced, but synaptophysin mrna and protein were not altered. feeding the high-sucrose diet for weeks did not change pge txb or ltb concentration significantly. because the 8-week high-sucrose feeding paradigm represents early-stage metabolic syndrome in the absence of pathological diabetes or obesity, these findings demonstrate changes in brain pufa metabolizing enzymes and composition in association with reduced bdnf and drebrin mrna at an early disease stage. the upregulation of brain cpla and ipla enzyme activities in the high-sucrose fed rats suggests an increase in brain aa and dha metabolism. in this regard, disturbed saturated brain fatty acid metabolism has been reported in humans and rats with the metabolic syndrome. a positron emission tomography study demonstrated increased brain uptake of 11c]palmitate and 18f]fluoro-6-thia-heptadecanoic acid in patients with the metabolic syndrome. hypothalamic concentrations of long-chain saturated acyl-coas were increased in a high-fat diet animal model of the metabolic syndrome, also indicating increased metabolism of long-chain saturated fatty acids. taken together, the results suggest non-specific upregulation in brain fatty acid metabolism, including pufas, associated with the metabolic syndrome. upregulated aa or dha metabolism could be directly confirmed in this animal model, using quantitative autoradiography to image fatty acid uptake following radiotracer injection, or can be examined in humans using positron emission tomography. the released fatty acids may be alternative energy substrates to glucose for brain metabolism, due to cerebral hypoglycemia caused by insulin-resistance. this is consistent with evidence of increased brain activity of carnitine palmitoyltransferase in an animal model of the metabolic syndrome. 14c-palmitate conversion to 14c-co also was increased in mitochondrial brain extracts of diabetic mice. brain cpla activity and phospho-cpla protein, a marker of activated cpla, were increased in the high-sucrose fed rats in the absence of changes in cpla mrna or protein, suggesting post-translational modification and upregulated brain aa metabolism, consistent with the increased unesterified aa concentration. increased activation of cpla may reflect excitotoxicity associated with increased influx of extracellular calcium into the cell via ionotropic glutamatergic receptors. since cpla also is functionally coupled via g-proteins to dopaminergic, serotonergic and muscarinic neuroreceptors, an increase in its activity suggests disturbed g-protein neuroreceptor signaling in the metabolic syndrome. cytokine receptor activation may also initiate cpla activation, although our findings do not suggest an increase in cytokine expression in rats fed the high-sucrose diet. ipla is insensitive to extracellular calcium influx into the neuron, but can be activated by intracellular calcium released from the endoplasmic reticulum by the calcium-releasing ryanodine receptor. mobilization of intracellular calcium stores can be mediated by increased intracellular unesterified aa levels, which was reported to activate the ryanodine receptor in vitro. this is in agreement with the finding that the unesterified aa concentration was increased in the high-sucrose diet rats. likely, this increase in aa concentration occurred intracellularly, since spla which releases aa extracellularly, was not changed significantly. concentrations of pro-inflammatory eicosanoids did not differ between the groups. it is possible, however, that changes in eicosanoids or cytokines occurred in specific brain regions such as the hippocampus, as reported in genetically diabetic mice, or that longer administration of the high-sucrose diet sufficient to initiate diabetes would increase whole brain cytokine levels. however, consistent with the lack of significant changes in the three eicosanoids, we did not find significant changes in mrna levels for cox- cox- 5- or 15-lox in the high-sucrose fed rats, nor in tnf-α or gfap mrna, suggesting the absence of neuroinflammation, since transcription of these molecular markers occurs within transcriptional circuits related to neuroinflammation. whole brain bdnf mrna and protein levels were reduced in the high-sucrose group, in agreement with previous studies that showed reduced bdnf levels in animal models of the metabolic syndrome with behavioral impairment. reduced bdnf expression was not mediated by pro-inflammatory eicosanoids, which were not changed. one possibility is that the increased unesterified aa concentration in the high-sucrose animals decreased bdnf and induced apoptosis, as reported in cultured spinal cord neurons. reduced bdnf expression in the sucrose-fed rats may have promoted dendritic injury, which was indirectly suggested by the reduction in drebrin mrna, or have altered the cellular dynamics and structural organization of dendritic spines in the absence of changes in drebrin protein. changes in dendritic morphology and dynamics could be the topic of future studies. additionally, more severe changes in synaptic structure are likely to occur with prolonged exposure to the high-sucrose diet, since the 8-week feeding paradigm causes only early-stage metabolic syndrome without obesity, diabetes or liver damage. contrary to reports using other models involving central insulin resistance, we did not find evidence of phospholipid degradation in the brain, since phospholipid mass, derived by the summation of total fatty acids within each phospholipid class, did not differ between the dietary groups. also, lysopc, a marker of phospholipid breakdown, was not changed. the changes in phospholipid fatty acid concentrations were relatively minor, and were significant only for a few n- pufas in etngpl and in lysopc.  in summary, brain enzymatic markers of aa and dha metabolism were increased in a rat model of early-stage metabolic syndrome, in association with reduced bdnf mrna and protein, and drebrin mrna. increases in cpla and ipla activities support the notion of phospholipase-mediated neurodegeneration. the decreases in bdnf and drebrin suggest increased susceptibility to synapto-dendritic injury. in the future, an upregulation in brain aa and dha metabolism associated with the metabolic syndrome might be imaged in humans with positron-emitting tomography using radiolabeled aa or dha, as biomarkers of disease progression. therapeutic strategies aimed at downregulating brain pufa metabolism, such as the administration of carnitine palmitoyltransferase inhibitors or pla inhibitors, might be effective in slowing the progression of brain lipid abnormalities identified in this study, the associated changes in synaptic loss and possibly, cognitive dysfunction in the metabolic syndrome. 
the concentration of several n- fatty acids in ethanolamine glycerophospholipids and lysophosphatidylcholine was increased, as was unesterified aa concentration. in animal models, the metabolic syndrome elicits a cerebral response characterized by altered phospholipid and unesterified fatty acid concentrations and increases in pro-apoptotic inflammatory mediators that may cause synaptic loss and cognitive impairment. these findings show upregulated brain aa and dha metabolism and reduced bdnf and drebrin, but no changes in eicosanoids, in an animal model of the metabolic syndrome. the high-sucrose compared with control diet induced insulin resistance, and increased phosphorylated-cpla protein, cpla and ipla activity and 12-lipoxygenase mrna, but decreased bdnf mrna and protein, and drebrin mrna. brains were assayed for markers of aa metabolism, dha metabolism, brain-derived neurotrophic factor, and synaptic integrity. these changes might contribute to altered synaptic plasticity and cognitive impairment in rats and humans with the metabolic syndrome. arachidonic aciddocosahexaenoic acidbdnfbrainpolyunsaturated fatty acids metabolic syndromedrebrinsucroseinsulin resistance male wistar rats were fed a control or high-sucrose diet for weeks. we hypothesized that these changes are associated with phospholipase enzymes that regulate arachidonic and docosahexaenoic acid metabolism, major polyunsaturated fatty acids in brain.
 in animal models, the metabolic syndrome elicits a cerebral response characterized by altered phospholipid and unesterified fatty acid concentrations and increases in pro-apoptotic inflammatory mediators that may cause synaptic loss and cognitive impairment. we hypothesized that these changes are associated with phospholipase enzymes that regulate arachidonic and docosahexaenoic acid metabolism, major polyunsaturated fatty acids in brain. male wistar rats were fed a control or high-sucrose diet for weeks. brains were assayed for markers of aa metabolism, dha metabolism, brain-derived neurotrophic factor, and synaptic integrity. lipid concentrations were measured in brains subjected to high-energy microwave fixation.  the high-sucrose compared with control diet induced insulin resistance, and increased phosphorylated-cpla protein, cpla and ipla activity and 12-lipoxygenase mrna, but decreased bdnf mrna and protein, and drebrin mrna. the concentration of several n- fatty acids in ethanolamine glycerophospholipids and lysophosphatidylcholine was increased, as was unesterified aa concentration. eicosanoid concentrations did not change.  these findings show upregulated brain aa and dha metabolism and reduced bdnf and drebrin, but no changes in eicosanoids, in an animal model of the metabolic syndrome. these changes might contribute to altered synaptic plasticity and cognitive impairment in rats and humans with the metabolic syndrome. arachidonic aciddocosahexaenoic acidbdnfbrainpolyunsaturated fatty acids metabolic syndromedrebrinsucroseinsulin resistance 