Search

In mild cognitive impairment (MCI) due to Alzheimer disease (AD), also known as prodromal AD, there is evidence for a pathologic shortage of uridine, choline, and docosahexaenoic acid [DHA]), which are key nutrients needed by the brain. Preclinical and clinical evidence shows the importance of nutrient bioavailability to support the development and maintenance of brain structure and function in MCI and AD. Availability of key nutrients is limited in MCI, creating a distinct nutritional need for uridine, choline, and DHA. Evidence suggests that metabolic derangements associated with ageing and disease-related pathology can affect the body’s ability to generate and utilize nutrients. This is reflected in lower levels of nutrients measured in the plasma and brains of individuals with MCI and AD dementia, and progressive loss of cognitive performance. The uridine shortage cannot be corrected by normal diet, making uridine a conditionally essential nutrient in affected individuals. It is also challenging to correct the choline shortfall through diet alone, because brain uptake from the plasma significantly decreases with ageing. There is no strong evidence to support the use of single-agent supplements in the management of MCI due to AD. As uridine and choline work synergistically with DHA to increase phosphatidylcholine formation, there is a compelling rationale to combine these nutrients. A multinutrient enriched with uridine, choline, and DHA developed to support brain function has been evaluated in randomized controlled trials covering a spectrum of dementia from MCI to moderate AD. A randomized controlled trial in subjects with prodromal AD showed that multinutrient intervention slowed brain atrophy and improved some measures of cognition. Based on the available clinical evidence, nutritional intervention should be considered as a part of the approach to the management of individuals with MCI due to AD, including adherence to a healthy, balanced diet, and consideration of evidence-based multinutrient supplements.

The human pineal is an unpaired midline organ, derived from and surrounded by brain tissue, which secretes a hormone, melatonin, into the blood and the cerebrospinal fluid, principally during the daily dark period. The melatonin then activates receptors on brain neurons to provide a time-signal for various circadian rhythms, to promote sleep onset, and principally, sleep maintenance during the night. The deficiency in nocturnal plasma melatonin levels that often occurs among older people, caused by the unexplained tendency of their pineals to develop progressive calcification, is a frequent cause of decreased sleep efficiency, manifest as the tendency to awaken for prolonged periods during the night. This can be treated by “hormone replacement therapy” using small doses of oral melatonin, just sufficient to raise its blood levels to what they were nocturnally earlier in life. Melatonin's synthesis starts with the 5-hydroxylation of the essential amino acid tryptophan, followed by its decarboxylation to form serotonin (5-hydroxytryptamine). In the pineal, but to a very limited extent elsewhere in the body, this serotonin is converted to melatonin by enzymes that acetylate its amine nitrogen, forming N-acetylserotonin, which is then O-methylated to form the melatonin (5-methoxy-N-acetyltryptamine). When humans and other mammals are in darkness the electrical activity of, and norepinephrine release from, the pineal's sympathetic nerves are maximal, and the intrasynaptic norepinephrine acts on pineal beta receptors, forming cyclic-AMP and activating the enzymes that will convert the serotonin to melatonin. Conversely, exposure to environmental lighting diminishes the pineal's sympathetic activity and its synthesis of melatonin. In submammalian vertebrates the pineal organ often contains photoreceptors, through which light exposure can directly affect brain. Melatonin is highly lipid soluble: hence, it circulates largely bound to albumin, and it readily diffuses across cellular membranes in the brain and elsewhere.

Drugs that block muscarinic cholinergic neurotransmission in the brain can, as a consequence, increase the formation of amyloid-β, and decrease brain levels of phosphatidylcholine (by slowing its synthesis and accelerating its turnover). Both of these effects might cause a decrease in brain synapses, as characterizes and probably underlies the memory disorder of early Alzheimer's disease.

Numerous neurobehavioral diseases typically exhibit annual rhythms in the frequency with which they cause flare-ups. A prime example is the seasonal affective disorder syndrome (SADS), in which symptoms usually start to appear in November and disappear in the late winter, after which many patients remain asymptomatic until the following fall. Smaller seasonal variations in mood and behavior are also sometimes noted among patients with Depression, per se, but less so among normal control subjects.

Brain neurons form synapses throughout the life span. This process is initiated by neuronal depolarization, however the numbers of synapses thus formed depend on brain levels of three key nutrients—uridine, the omega-3 fatty acid DHA, and choline. Given together, these nutrients accelerate formation of synaptic membrane, the major component of synapses. In infants, when synaptogenesis is maximal, relatively large amounts of all three nutrients are provided in bioavailable forms (e.g., uridine in the UMP of mothers’ milk and infant formulas). However, in adults the uridine in foods, mostly present at RNA, is not bioavailable, and no food has ever been compelling demonstrated to elevate plasma uridine levels. Moreover, the quantities of DHA and choline in regular foods can be insufficient for raising their blood levels enough to promote optimal synaptogenesis. In Alzheimer’s disease (AD) the need for extra quantities of the three nutrients is enhanced, both because their basal plasma levels may be subnormal (reflecting impaired hepatic synthesis), and because especially high brain levels are needed for correcting the disease-related deficiencies in synaptic membrane and synapses., National Institutes of Health (U.S.)

aDepartment of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge *Corresponding author: Richard J. Wurtman, MD, Massachusetts Institute of Technology, Department of Brain and Cognitive Sciences, Bldg 46-5023, Cambridge, MA 02139 (dick@mit.edu). J Clin Psychiatry 2015;76(12):e1619–e1621 dx.doi.org/10.4088/JCP.15com10380 © Copyright 2015 Physicians Postgraduate Press, Inc. M patients suffering from depression are also overweight, or even obese,1–3 and the comorbidity of depression and diabetes—frequently caused by obesity— is even greater.4 This association has raised the possibility that a particular gene can, in some patients, confer vulnerability to both conditions.5 Some evidence supports this hypothesis.5 In the present issue of the Journal, Samaan and associates5 confirmed that a high body mass index was positively correlated with depression status and found that 1 of 21 genetic variants (single nucleotide polymorphisms) was associated with both obesity and major depression. In an earlier study in twins,6 the authors found that 12% of the genetic component of depression was shared with obesity. This indicates that the relationship between depression and obesity must also be generated by nongenetic factors, probably including the following 3 groups proposed

Novel approaches for studying the brain and relating its activities to mental phenomena have come into use during the past decade (Bargmann, 2015). These include both new laboratory methods – involving, among others, generation of isolated cells which retain neuronal characteristics in vivo; the selective stimulation of neurons by light in vivo; and direct electrical stimulation of specific brain regions to restore a system's balance of excitation and inhibition – and a new organizing principle, “connectomics”, which recognizes that networks, and not simply a key nucleus or region, underlie most brain functions and malfunctions. Its application has already improved our comprehension of how the brain normally functions and our ability to help patients with such poorly treated neurologic and psychiatric diseases as Alzheimer's disease.

Brain phosphatide synthesis requires three circulating compounds: docosahexaenoic acid (DHA), uridine, and choline. Oral administration of these phosphatide precursors to experimental animals increases the levels of phosphatides and synaptic proteins in the brain and per brain cell as well as the numbers of dendritic spines on hippocampal neurons. Arachidonic acid fails to reproduce these effects of DHA. If similar increases occur in human brain, administration of these compounds to patients with diseases that cause loss of brain synapses, such as Alzheimer's disease, could be beneficial.

Alzheimer's disease (AD) is a progressive condition characterized by neurodegeneration and the dense deposition of proteins in the brain. There is no cure for AD and current treatments usually only provide a temporary reduction of symptoms. There is thus a strong unmet need for effective preventative and therapeutic strategies and the potential role for nutrition in such strategies is rapidly gaining interest. An Alzheimer's brain contains fewer synapses and reduced levels of synaptic proteins and membrane phosphatides. Brain membrane phosphatide synthesis requires at least three dietary precursors: polyunsaturated fatty acids, uridine monophosphate (UMP) and choline. Animal studies have shown that administration of these nutrients increases the level of phosphatides, specific pre- or post-synaptic proteins and the number of dendritic spines - a requirement for new synapse formation. These effects are markedly enhanced when animals receive all three compounds together. This multi-nutrient approach in animals has also been shown to decrease amyloid beta protein (Abeta) plaque burden, improve learning and memory through increased cholinergic neurotransmission and have a neuroprotective effect in several mouse models of AD. Whether these potential therapeutic effects of a multi-nutrient approach observed in animal models can also be replicated in a clinical setting warrants further investigation.

The synthesis of neurotransmitters in mammalian brain responds rapidly to changes in precursor availability. Serotonin synthesis depends largely on the brain concentrations of l-tryptophan, its precursor amino acid. This relationship appears to be physiologic: when brain tryptophan levels vary because of insulin secretion or meal ingestion, corresponding alterations occur in the rate of serotonin formation. The ability of any food to modify brain tryptophan (and serotonin) depends on how its ingestion changes the serum concentrations of not only tryptophan, but also several other large neutral amino acids that compete with tryptophan for uptake into the brain. Such precursorinduced changes in brain serotonin appear to be functionally important: animals having a reduced level of brain serotonin (caused by the chronic ingestion of a naturally tryptophan-poor diet, such as corn) demonstrate a heightened sensitivity to painful stimuli; this pain sensitivity can be acutely restored to normal values by a single injection of L-tryptophan, which rapidly elevates brain serotonin. The synthesis of catecholamines (e.g., dopamine, norepinephrine) in the brain also varies with the availability of the precursor amino acid L-tyrosine. Single injectionsof this amino acid increase brain tyrosine levels and accelerate brain catechol synthesis, while injections of a competing neutral amino acid (e.g., leucine, tryptophan) reduce brain tyrosine and its rate of conversion to dopa. The rate of catecholamine synthesis, however, appears to be influenced less by precursor levels than is serotonin formation: tymsine hydroxylase, which catalyzes the ratelimiting step in catecholamine synthesis, responds strongly to end-product inhibition and to other controls that reflect variations in neuronal activity. The synthesis of acetylcholine in brain responds to substrate (choline) availability much like serotonin synthesis. Short-term alterations in brain choline levels are mirrored by similar changes in brain acetylcholine concentration. Variations in the daily dietary intake of choline also modify brain choline and acetylcholine. The relationship between choline availability and acetylchoiine synthesis has already found a clinical application: choline has been used successfully in the treatment of tardive dyskinesia, a disorder of the central nervous system thought to reflect a deficiency in cholinergic transmission. These relationships between precursor availability from the periphery and brain neurotransmitter synthesis may ultimately provide the brain with information about peripheral metabolic state.

Docosahexaenoic acid (DHA), an omega-3 polyunsaturated fatty acid, is an essential component of membrane phosphatides and has been implicated in cognitive functions. Low levels of circulating or brain DHA are associated with various neurocognitive disorders including Alzheimer’s disease (AD), while laboratory animals, including animal models of AD, can exhibit improved cognitive ability with a diet enriched in DHA. Various cellular mechanisms have been proposed for DHA’s behavioral effects, including increases in cellular membrane fluidity, promotion of neurite extension, and inhibition of apoptosis. However, there is little direct evidence that DHA affects synaptic structure in living animals. Here we show that oral supplementation with DHA substantially increases the number of dendritic spines in adult gerbil hippocampus, particularly when animals are co-supplemented with a uridine source, uridine-5’-monophosphate (UMP), which increases brain levels of the rate-limiting phosphatide precursor CTP. The increase in dendritic spines (> 30%) is accompanied by parallel increases in membrane phosphatides, and in pre- and post-synaptic proteins within the hippocampus. Hence oral DHA may promote neuronal membrane synthesis to increase the number of synapses, particularly when co-administered with UMP. Our findings provide a possible explanation for the effects of DHA on behavior and also suggest a strategy to treat cognitive disorders resulting from synapse loss.

The synthesis of phospholipids in mammalian cells is regulated by the availability of three critical precursor pools: those of choline, cytidine triphosphate and diacylglycerol. Diacylglycerols containing polyunsaturated fatty acids (PUFAs) apparently are preferentially utilized for phosphatide synthesis. PUFAs are known to play an important role in the development and function of mammalian brains. We therefore studied the effects of unsaturated, monounsaturated and polyunsaturated fatty acids on the overall rates of phospholipid biosynthesis in PC12 rat pheochromocytoma cells. Docosahexaenoic acid (DHA, 22:6n-3), eicosapentaenoic acid (EPA, 20:5n-3) and arachidonic acid (AA, 20:4n-6) all significantly stimulated the incorporation of 14C-choline into total cellular phospholipids. In contrast, monounsaturated oleic acid (OA) and the saturated palmitic (PA) and stearic (SA) acids did not have this effect. The action of DHA was concentration-dependent between 5 and 50 μM; it became statistically significant by 3 h after DHA treatment and then increased over the ensuing 3 h. DHA was preferentially incorporated into phosphatidylethanolamine (PE) and phosphatidylserine (PS), while AA predominated in phosphatidylcholine (PC).

The biosynthesis of brain membrane phosphatides, e.g., phosphatidylcholine (PtdCho), may utilize three circulating compounds: choline, uridine (a precursor for UTP, CTP, and CDP-choline), and a PUFA (e.g., docosahexaenoic acid); moreover, oral administration of the uridine source uridine-5'-monophosphate (UMP) can significantly increase levels of the phosphatides throughout the rodent brain. Since PtdCho can provide choline for acetylcholine (ACh) synthesis, we determined whether UMP administration also affects ACh levels in striatum and striatal extracellular fluid, in aged and young rats. Among aged animals consuming a UMP-containing diet (2.5%, w/w) for 1 or 6 weeks, baseline ACh levels in striatal dialysates rose from 73 fmol/min to 148 or 197 fmol/min (P

We have previously shown that chronic, but not acute, dietary supplementation with CDP-choline prevents the hippocampal-dependent memory deficits manifested by aged rats and by rats reared under impoverished environmental conditions. In rats, dietary CDP-choline is rapidly metabolized into cytidine and choline; the cytidine is then readily converted to uridine, which enters the brain and, via conversion to UTP and CTP, increases brain levels of membrane phosphatides. Hence, we have assessed whether administering a uridine source (UMP) instead of CDP-choline can also ameliorate the memory deficits in rats reared under impoverished environmental conditions. At weaning, 32 male Sprague-Dawley rats were exposed to either enriched (EC) or impoverished (IC) conditions for 3 mo. Concurrently, IC and EC rats were given access to either a control diet or a diet supplemented with 0.1% UMP. Rats were then assessed for learning and memory skills using 2 versions of the Morris water maze, the hidden platform version that assesses hippocampal-dependent cognitive memory processing, and the visible platform version that assesses striatal-dependent habit memory. As expected, exposure to the impoverished environment impaired hippocampal-dependent, but not striatal-dependent learning and memory. Supplementation with UMP prevented this cognitive dysfunction, as had been observed with supplemental CDP-choline. These results suggest that IC rats do not use and/or remember their spatial strategies for task solving as well as EC rats, and that long-term dietary supplementation with UMP alleviates this dysfunction.

Evidence suggests that platelet-activating factor (PAF) is a mediator in inflammatory-based pain. Using the biphasic formalin model in rats, we recently demonstrated that PAF antagonists which were selective for either intracellular or plasma membrane PAF receptors decreased the late-phase of the nociceptive response. Inasmuch as both of the PAF antagonists previously used were administered systemically, and reportedly are able to cross the blood-brain barrier, the anatomic locations at which PAF affects pain processing remained to be elucidated. Since PAF is required for hippocampal-dependent memory consolidation, and since the hippocampus has been shown to mediate the late-phase of formalin-induced nociception, the present study investigated the effects on nociception of administration of PAF antagonists within the hippocampus, and of using agents specific for either plasma membrane (BN 52021) or intracellular (BN 50730) PAF binding sites. Intrahippocampal injections of BN 52021 decreased the late-phase of the nociceptive response in a concentration-dependent manner. In contrast, intrahippocampal administration of BN 50730 had no effect on inflammatory nociception. These findings suggest that hippocampal plasma membrane PAF receptors, but not intracellular PAF binding sites, mediate tonic inflammatory pain processing in rats.

Epidemiological studies demonstrate a relationship between statin [3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor] usage and reduced risk of developing Alzheimer's disease. To determine whether statins affect neuronal development, we treated cultured rat hippocampal neurons with pravastatin. After 4-48 h of treatment, pravastatin significantly increased the number of neurites produced by each cell and caused a corresponding increase in levels of the membrane phospholipid phosphatidylcholine. Pravastatin treatment also significantly increased neurite length and branching but did not affect cellular cholesterol levels. Co-incubation with mevalonate, but not cholesterol, abolished the stimulatory effect of pravastatin on neurite outgrowth. Treatment of neurons with isoprenoids also abolished the effect of pravastatin on neurite growth, suggesting that pravastatin may stimulate neuritogenesis by preventing isoprenylation of signaling molecules such as the Rho family of small GTPases. A specific inhibitor of geranylgeranylation, but not farnesylation, mimicked the stimulatory effect of pravastatin on neuritogenesis. Pravastatin treatment significantly decreased levels of membrane-associated RhoA. These data suggest that pravastatin treatment increases neurite outgrowth and may do so via inhibiting the activity of geranylgeranylated proteins such as RhoA.

Item does not contain fulltext Recently, a biomarker panel of 10 plasma lipids, including 8 phosphatidylcholine species, was identified that could predict phenoconversion from cognitive normal aged adults to amnestic mild cognitive impairment or Alzheimer's disease (AD) within 2-3 years with >90% accuracy. The reduced levels of these plasma phospholipids could reflect altered phospholipid metabolism in the brain and periphery. We show that a 24-week nutritional intervention in drug-naive patients with very mild to mild AD significantly increased 5 of the 7 measured biomarker phosphatidylcholine species. By providing nutrients which normally rate-limit phospholipid synthesis, this nutritional intervention could be useful in asymptomatic subjects with a plasma lipid biomarker profile prognostic of AD.

A relationship between genetic makeup and susceptibility to major depressive disorder (MDD) has long been suspected on the basis of family and twin studies. A metaanalysis of reports on the basis of twin studies has estimated MDD's degree of heritability to be 0.33 (confidence interval, 0.26-0.39). Among families exhibiting an increased prevalence of MDD, risk of developing the illness was enhanced in members exposed to a highly stressful environment. Aberrant genes can predispose to depression in a number of ways, for example, by diminishing production of growth factors that act during brain development. An aberrant gene could also increase or decrease a neurotransmitter's release into synapses, its actions, or its duration of activity. The gene products of greatest interest at present are those involved in the synthesis and actions of serotonin; among them, the serotonin-uptake protein localized within the terminals and dendrites of serotonin-releasing neurons. It has been found that the Vmax of platelet serotonin uptake is low in some patients with MDD; also, Vmax is highly correlated in twins. Antidepressant drugs such as the selective serotonin reuptake inhibitors act on this uptake protein. The specific genetic locus causing serotonin uptake to be lower in some patients with major depression involves a polymorphic region (5-HTTLPR) in the promoter region of the gene for the uptake protein. The gene itself exists as several alleles, the short "S" allele and the long "L" allele. The S variant is associated with less, and the L variant with more, of the uptake protein. The effect of stressful life events on depressive symptoms in young adults was found to be significantly stronger among SS or SL subjects than among LL subjects. Neuroimaging studies showed that people with the SS or SL alleles exhibited a greater activation of the amygdala in response to fearful stimuli than those with LL. It has been reported recently that mutations in the gene that controls serotonin synthesis in the human brain (tryptophan hydroxylase) also predispose to mood disturbances. It may be asked whether people who lack a psychiatric history should be advised to avoid stressful environments if they are found to carry the SS or SL alleles.

During rapid cell growth the availability of phospholipid precursors like cytidine triphosphate and diacylglycerol can become limiting in the formation of key membrane constituents like phosphatidylcholine. Uridine, a normal plasma constituent, can be converted to cytidine triphosphate in PC12 [corrected] cells and intact brain, and has been shown to produce a resulting increase in phosphatidylcholine synthesis. To determine whether treatments that elevate uridine availability also thereby augment membrane production, we exposed PC12 [corrected] cells which had been differentiated by nerve growth factor to various concentrations of uridine, and measured the numbers of neurites the cells produced. After 4 but not 2 days uridine significantly and dose-dependently increased the number of neurites per cell. This increase was accompanied by increases in neurite branching and in levels of the neurite proteins neurofilament M [corrected] and neurofilament 70. Uridine treatment also increased intracellular levels of cytidine triphosphate, which suggests that uridine may affect neurite outgrowth by enhancing phosphatidylcholine synthesis. Uridine may also stimulate neuritogenesis by a second mechanism, since the increase in neurite outgrowth was mimicked by exposing the cells to uridine triphosphate, and could be blocked by various drugs known to antagonize P2Y receptors (suramin; Reactive Blue 2; pyridoxal-phosphate-6-azophenyl-2',4' disulfonic acid). Treatment of the cells with uridine or uridine triphosphate stimulated their accumulation of inositol phosphates, and this effect was also blocked by pyridoxal-phosphate-6-azophenyl-2',4' disulfonic acid. Moreover, degradation of nucleotides by apyrase blocked the stimulatory effect of uridine on neuritogenesis. Taken together these data indicate that uridine can regulate the output of neurites from differentiating PC12 [corrected] cells, and suggest that it does so in two ways, i.e. both by acting through cytidine triphosphate as a precursor for phosphatidylcholine biosynthesis and through uridine triphosphate as an agonist for P2Y receptors.

We investigated the effects of prostaglandin E2 (PGE2) on amyloid precursor protein (APP) expression in cultured rat microglia. PGE2 treatment significantly increased the expression of APP holoprotein and was associated with an elevation in cyclic AMP (cAMP). Direct activation of adenylate cyclase with forskolin also increased APP expression. Co-treatment of microglia with PGE2 and the PKA inhibitor H-89 suppressed the overexpression of APP caused by PGE2 alone. The prostaglandin EP2 receptor is known to be positively coupled to cAMP production. Stimulation of the EP2 receptor with butaprost increased APP holoprotein, whereas co-incubation of the cells with PGE2 and the EP2 receptor antagonist AH-6809 blocked the effect of PGE2 on APP expression. These data suggest that PGE2 is able to regulate the expression of APP, and that this effect may be mediated by the EP2 receptor and the cAMP signaling cascade.

Giving L-tryptophan, serotonin's circulating precursor, or a serotonin-releasing drug can decrease food intake and body weight. Giving 5-hydroxy-L-tryptophan (5-HTP), serotonin's immediate intracellular precursor, has been thought to be ineffective in enhancing brain serotonin synthesis unless it is coadministered with a dopa decarboxylase inhibitor to protect 5-HTP from destruction outside the brain. We have examined the effect of 5-HTP on food consumption and tissue 5-HTP levels among rats subjected to two different hyperphagic stimuli, food deprivation and a standardized stress (tail pinch), and on plasma 5-HTP levels in humans. In rats, 5-HTP (3-200 mg/kg ip) suppressed food intake in a dose-dependent manner in both models, but was at least eight times more effective in our stress-hyperphagia model. (Differences in the two procedures might have contributed to the observed differences in potencies.) This suppression was blocked by coadministration of another large neutral amino acid (LNAA), L-valine. Brain 5-HTP levels correlated significantly with peak plasma 5-HTP (r(2)=.69) or 5-HTP/LNAA (r(2)=.81) levels. Additionally, among humans, oral 5-HTP (1.2-2.0 mg/kg) produced, after 1 and 2 h, a significant increase in plasma 5-HTP (1.5- to 2.3-fold). These observations suggest that 5-HTP may be useful in controlling the excessive food intake sometimes generated by stress, even if given without decarboxylase inhibitors or other drugs.

Patients exhibiting the classic manifestations of parkinsonism - tremors, rigidity, postural instability, slowed movements and, sometimes, sleep disturbances and depression - may also display severe cognitive disturbances. All of these particular motoric and behavioral symptoms may arise from Parkinson's disease [PD] per se, but they can also characterize Lewy Body dementia [LBD] or concurrent Parkinson's and Alzheimer's diseases [PD & AD]. Abnormalities of both movement and cognition are also observed in numerous other neurologic diseases, for example Huntington's Disease and the frontotemporal dementia. Distinguishing among these diseases in an individual patient is important in "personalizing" his or her mode of treatment, since an agent that is often highly effective in one of the diagnoses (e.g., L-dopa or muscarinic antagonists in PD) might be ineffective or even damaging in one of the others. That such personalization, based on genetic, biochemical, and imaging-based biomarkers, is feasible is suggested by the numerous genetic abnormalities already discovered in patients with parkinsonism, Alzheimer's disease and Huntington's disease (HD) and by the variety of regional and temporal patterns that these diseases can produce, as shown using imaging techniques.

The phospholipid mediator platelet-activating factor (PAF), and its non-hydrolyzable analog methylcarbamyl-PAF (mc-PAF) increase prostaglandin E(2) (PGE(2)) release from astrocyte-enriched cortical cell cultures. Cyclooxygenase (COX) enzymes--of which there are two known isoforms--convert arachidonic acid to prostaglandin (PG) H(2) (PGH(2)), which is further metabolized to various PGs, including PGE(2). COX-1 is generally considered to contribute to cell homeostasis, whereas COX-2 is thought to mediate inflammatory/immune PG formation. In this study we examined the involvement of the COX isoforms in PAF-induced PGE(2) release. Treatment of cells with the non-specific COX inhibitor indomethacin, or the specific COX-2 inhibitor NS-398, prior to mc-PAF stimulation completely blocked the PAF-induced release of PGE(2); treatment with more selective COX-1 inhibitors (i.e. piroxicam and SC-560) failed to significantly do so. These data suggest that COX-2 is responsible for PAF-mediated PGE(2) release in primary astrocytes.

The uridine nucleotides uridine-5'-triphosphate (UTP) and uridine-5'-diphosphate (UDP) have previously been identified in media from cultured cells. However, no study to date has demonstrated their presence in brain extracellular fluid (ECF) obtained in vivo. Using a novel method, we now show that UTP and UDP, as well as uridine, are detectable in dialysates of striatal ECF obtained from freely-moving rats. Intraperitoneal (i.p.) administration of uridine or exposure of striatum to depolarizing concentrations of potassium chloride increases extracellular uridine, UTP and UDP, while tetrodotoxin (TTX) decreases their ECF levels. Uridine administration also enhances cholinergic neurotransmission which is accompanied by enhanced brain levels of diacylglycerol (DAG) and inositol trisphosphate (IP3) and blocked by suramin, but not by PPADS (pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid) or MRS2578 suggesting a possible mediation of P2Y2 receptors activated by UTP. These observations suggest that uridine, UTP and UDP may function as pyrimidinergic neurotransmitters, and that enhancement of such neurotransmission underlies pharmacologic effects of exogenous uridine on the brain. (C) 2014 Elsevier Ltd. All rights reserved.

Sprague-Dawley rats were reared in enriched (EC; group housing, exposure to stimulating objects, frequent handling) or restricted (RC; individual housing, no exposure to stimulating objects, minimal handling) environments starting on day 23 of life. At six months of age, they underwent behavioural tests to assess ‘cognitive’ and ‘stimulus-response’ memory, selective attention, and inflammatory pain processing. Alterations in synapses and cell survival may occur as a result of environment differences; therefore we assessed the brain levels of several proteins implicated in neurite outgrowth, synaptogenesis, and cell survival. Brains were dissected and analysed for amyloid precursor protein (APP) and other synaptic and cytoskeletal proteins using Western blotting. The performance of EC animals in a hidden platform water maze task, and in a test of selective attention (both of which are thought to involve the hippocampus) was superior to that of RC animals. In contrast, performance of RC animals on two stimulus-response tasks, the visible platform water maze test and simple visual discrimination (both of which are thought to be hippocampal independent) was indistinguishable from that of EC animals. Male EC rats displayed a different behavioural response to formalin during the inflammatory phase of nociception ‐ the phase affected by hippocampal processing; a similar trend was observed in females. Female but not male RC rats exhibited elevated plasma corticosterone levels; adrenal weights were unaffected by environmental conditions. Region-specific increases in brain levels of APP, neurofilament-70 (NF-70), and platelet-activating factor receptor (PAF-R) were found in EC rats. These data suggest that enriched animals manifest enhanced functioning of certain hippocampus-mediated behaviours when compared with that of their restricted counterparts; and that brain levels of various synaptic and structural proteins involved in neurite outgrowth, cell survival, and synaptogenesis, are affected by environmental factors.

We examined the effects of orally administered 5'-cytidinediphosphocholine (CDP-choline) on arterial plasma choline and cytidine levels and on brain phospho- lipid composition in rats . Animals receiving a single oral dose of 100, 250, or 500 mg/kg showed peak plasma choline levels 6-8 h after drug administration (from 12 1 to 17 ± 2, 19 ± 2, and 24 ± 2 pM, respectively) . The area under the plasma choline curve at >14 IiM,i.e., at a concentration that induces a net influx of choline into the brain, was significantly correlated with CDP-choline dose .In rats receiving 500 mg/kg this area was 2 .3 times that of animals consuming 250 mg/kg, which in turn was 1 .8 times that of rats receiving 100 mg/kg . Plasma cyti- dine concentrations increased 5 .4, 6 .5, and 15 .1 times baseline levels, respectively, 8 h after each of the three doses . When the oral CDP-choline treatment was pro- longed for 42 and 90 days, brain phosphatidylcholine concentrations increased significantly (by 22-25% ; p < 0 .05) in rats consuming 500 mg/kg/day . Brain phos- phatidylethanolamine and phosphatidylserine concentra- tions also increased significantly under some experi- mental conditions ; levels of other phospholipids were

Neurotransmitter receptors that increase phosphatidylinositol hydrolysis generate second messengers that activate protein kinase C. Here, we used metabotropic glutamate receptor agonists to increase both phosphatidylinositol hydrolysis and secretion of the soluble extracellular fragment of amyloid precursor protein (APPs) from cortical astrocyte cultures. The increase in APPs secretion was mimicked by direct activation of protein kinase C with phorbol ester and was suppressed by the metabotropic glutamate receptor antagonist l-(+)-2-amino-3-phosphonopropionic acid or by the protein kinase C inhibitor GF109203X. Ionotropic glutamate agonists did not increase APPs secretion. Forskolin or dibutyryl cyclic AMP inhibited the increase in APPs secretion caused by metabotropic glutamate receptor agonists or by phorbol ester treatment but did not affect basal APPs levels. Therefore, glutamatergic agonists that increase protein kinase C activation or decrease cyclic AMP formation may enhance the conversion of full-length APP to nonamyloidogenic APPs in Alzheimer's disease.

Rationale: Platelet-activating factor (PAF) is a membrane-derived phospholipid mediator that has biological effects on a variety of cells and tissues. A variety of stimuli, including those producing inflammation, promote the synthesis and release of PAF from various cell types. Evidence suggests that PAF exerts cellular actions through a plasma membrane receptor as well as via intracellular (microsomal) PAF binding sites. Objective: The present study was designed to: 1) investigate the role of PAF in a model of inflammatory nociception in rats (i.e. the formalin test), and 2) localize PAF's site(s) of action in nociception. To do this, we assessed the effect of administering two PAF antagonists (BN 52021 and BN 50730, which are selective for cell surface and intracellular PAF binding sites, respectively) on formalin-induced nociceptive responses. Methods: Forty minutes prior to formalin injection into the rat hindpaw, male Sprague-Dawley rats received systemic injections of BN 52021 (10, 1, or 0.1 mg/kg), BN 50730 (10, 1, or 0.1 mg/kg), or vehicle (45% 2-hydroxypropyl-β-cyclodextrin in distilled water, HBC) and the effects of the drugs on nociceptive behavioral responses were measured. Results: Rats receiving systemic BN 52021 or BN 50730 displayed a significant reduction of nociceptive responses in the late, but not early, phase of formalin-induced nociception. Conclusions: These findings suggest a role for endogenous PAF in nociceptive transmission, especially for persistent pain such as that which occurs in the late phase of the formalin test. The findings also indicate that both intracellular and cell surface PAF binding sites are involved in nociceptive modulation in rats, and that PAF antagonists might be useful for treating some patients with acute or chronic pain.

Stimulation of serotonin receptor subtypes 5-HT(2A) or 5-HT(2C) in stably transfected 3T3 cells by dexnorfenfluramine (DEXNOR) or serotonin increases secretion of the APP metabolite APP(s). It is not known whether activation of these receptors can also affect APP metabolism in vivo. We examined the effects of a single intraperitoneal (i.p.) injection of DEXNOR on APP(s) levels in cerebrospinal fluid (CSF) of guinea pigs. These levels were significantly (P0.05) increased by a single dose of DEXNOR (1-4 mg/kg); those of the APP metabolites Abeta(1-40) and Abeta(1-42) were unaffected. The DEXNOR-induced (1 mg/kg) increases in CSF APP(s) were suppressed by ritanserin (1 mg/kg) but not by ketanserin (2 mg/kg). When given alone, ritanserin did not affect CSF levels of APP(s), Abeta(1-40), or Abeta(1-42). Chronic treatment with DEXNOR for 9 days (1 mg/kg bid, i.p.) increased CSF APP(s) levels, measured 2 h after the last injection (P0.05), and decreased those of CSF Abeta(1-42) (P0.05). Neither hippocampal nor cortical levels of the APP holoprotein (APP(h)), nor body weight, were affected by DEXNOR. Chronic administration of mCPP (1-(m-chlorophenyl)piperazine) (2 mg/kg bid, i.p.), a 5-HT(2B/2C) agonist, for 9 days also increased CSF APP(s) levels (P0.5) when measured 2 h after the drug's last administration; hippocampal and cortical APP(h) levels were unaffected. However, mCPP also caused a significant decrease in body weight gain. These data indicate that the pharmacological activation of 5-HT(2C) receptors can stimulate CSF APP(s) secretion and reduce Abeta production in vivo. Hence 5-HT(2C) receptors, which apparently are localized to the brain, may represent useful targets for the development of treatments for Alzheimer's disease.

Psychologic states produced by environmental or physiologic stresses are usually associated with hypersecretion of adrenal hormones, particularly epinephrine and the glucocorticoids (hydrocortisone in humans or corticosterone in rats). A common mechanism links the secretion of these hormones, even though the adrenal medulla and cortex have different embryologic origins and biochemical properties and very different mechanisms controlling their secretory activities, ie, a cholinergic nervous input stimulates medullary secretion while a hormone, corticotropin (ACTH), activates secretion from the cortex. This mechanism is made possible by an intra-adrenal portal vascular system, which provides the medulla with uniquely high concentrations of glucocorticoids. These high concentrations are needed to induce the medullary enzyme, phenylethanolamine-N-methyltransferase (PNMT), which controls the synthesis of epinephrine from norepinephrine. By suppressing glucocorticoid secretion, pituitary failure compromises epinephrine synthesis and decreases the rate at which epinephrine is secreted; in contrast, prolonged chronic stress can enhance epinephrine synthesis and secretion within the adrenal, the brain, or both organs. This control mechanism could be involved in the long-term consequences of stress.

Traditionally Alzheimer's disease (AD) has been diagnosed and its course followed based on clinical observations and cognitive testing, and confirmed postmortem by demonstrating amyloid plaques and neurofibrillary tangles in the brain. But the growing recognition that the disease process is ongoing, damaging the brain long before clinical findings appear, has intensified a search for biomarkers that might allow its very early diagnosis and the objective assessment of its responses to putative treatments. At present at least eight biochemical measurements or scanning procedures are used as biomarkers, usually in panels, by neurologists and others. The biochemical measurements are principally of amyloid proteins and their A-beta precursors, or of tau proteins. Brain atrophy can be assessed by means of structural magnetic resonance imaging (sMRI), and decreased blood flow and metabolism can be estimated by functional magnetic resonance imaging (fMRI). [18F]fluorodeoxyglucose-positron emission tomography (FDG-PET) is used to measure the brain's energy utilization and to infer synaptic number. Impaired connectivity between brain regions is indicated by diffusion tensor imaging (DTI), while magnetic resonance spectroscopy (MRS) provides metabolic markers of diminished cell number. Additional proposed biomarkers utilize electroencephalography (EEG) and magnetoencephalography (MEG) for quantifying impairments in connectivity. Genetic analyses illustrate the heterogeneity of disease processes that can cause cognitive impairment syndromes. Recent observations awaiting confirmation suggest that levels of some plasma phospholipids can also be biomarkers of AD and that reductions in these levels can enable the accurate prediction that a cognitively normal individual will go on to develop MCI or AD within 2 years.

We measured, using microdialysis, the effects of sibutramine, given intraperitoneally, on brain dopamine and serotonin flux into striatal and hypothalamic dialysates of freely moving rats, and on the uptake of [(3)H]-DA into striatal synaptosomes. For microdialysis experiments, samples collected every 30 min were assayed by high-pressure liquid chromatography, in a single run. Administration of a low dose of sibutramine (2.0 mg/kg, i.p) had no effect on dopamine or serotonin concentrations in striatal dialysates but higher doses increased both: 5 mg/kg increased these concentrations to 196+/-24% (p

Twelve mildly hypertensive but otherwise normal fasting subjects received each of four treatments in random order: CDP-choline (citicoline; 500, 2000, and 4000 mg) or a placebo orally at 8:00 a.m. on four different treatment days. Eleven plasma samples from each subject, obtained just prior to treatment (8:00 a.m.) and 1–12 hr thereafter, were assayed for choline, cytidine, and uridine. Fasting terminated at noon with consumption of a light lunch that contained about 100 mg choline. Plasma choline exhibited dose-related increases in peak values and areas under the curves (AUCs), remaining significantly elevated, after each of the three doses, for 5, 8, and 10 hr, respectively. Plasma uridine was elevated significantly for 5–6 hr after all three doses, increasing by as much as 70–90% after the 500 mg dose, and by 100–120% after the 2000 mg dose. No further increase was noted when the dose was raised from 2000 to 4000 mg. Plasma cytidine was not reliably detectable, since it was less than twice blank, or less than 100 nM, at all of the doses. Uridine is known to enter the brain and to be converted to UTP; moreover, we found that uridine was converted directly to CTP in neuron-derived PC-12 cells. Hence, it seems likely that the circulating substrates through which oral citicoline increases membrane phosphatide synthesis in the brains of humans involve uridine and choline, and not cytidine and choline as in rats.

We examined the relationships between membrane phospholipid levels, the secretion and expression of the amyloid precursor protein (APP), and the responses of both to nerve growth factor (NGF), Abeta(1-40) or Abeta(40-1) in developing cortical neurons cultured from rat embryos. Neuronal membrane phospholipid levels per cell, and phosphatidylcholine, phosphatidylserine, phosphatidylinositol and phosphatidylethanolamine increased individually between the first and seventh days of culturing. The amounts of APP holoprotein and APP mRNAs in the cells, as well as the amounts of soluble APP (APPs) secreted by them, also increased during neuronal development in vitro. The increases in APPs exceeded the increases in APP which, in turn, exceed those in phospholipid levels. The levels of APP holoprotein, but not of phospholipids, increased when neurons were grown in a choline-free medium, suggesting that increases in APP are not sufficient to stimulate changes in membrane phospholipids. Treatment of neuron cultures for four days with NGF or Abeta(1-40), but not with Abeta(40-1), dose-dependently increased membrane phospholipids, tau and GAP-43, as well as APP holoprotein and secreted APPs. These results indicate that agents, like NGF or Abeta(1-40), which enhance membrane phospholipid levels may promote neurite formation, APP expression and APPs secretion in primary neuronal cultures.

We previously showed indirectly that the increase in diacylglycerol (DAG) levels caused by exposing differentiating PC12 cells to nerve growth factor (NGF) must derive mainly from de novo synthesis and, to a lesser and transient extent, from the hydrolysis of [3H]phosphatidylinositol (PI). To explore further the biochemical mechanisms of this increase, we measured, in PC12 cells, DAG synthesis from glycerol or various fatty acids; its liberation from phosphatidylcholine (PC); and the activities of various enzymes involved in DAG production and metabolism. Among cells exposed to NGF (0-116 h), the labeling of DAG from [3H]glycerol peaked earlier than that of [3H]PC, and the specific radioactivity of [3H]glycerol-labeled DAG was much higher than those of the [3H]phospholipids, indicating that [3H]DAG synthesis precedes [3H]phospholipid synthesis. NGF treatment also increased (by 50-330%) the incorporation of monounsaturated ([3H]oleic acid) and polyunsaturated ([14C]linoleic acid or [3H]arachidonic acid) fatty acids into DAG, and, by 15-70%, into PC. NGF treatment increased the activities of long chain acyl-CoA synthetases (LCASs), including oleoyl-CoA synthetase and arachidonoyl-CoA synthetase, by 150-580% over control, but cholinephosphotransferase activity rose by only 60%, suggesting that the synthesis of DAG in the cells was increased to a greater extent than its utilization. NGF did not promote the breakdown of newly formed [3H]PC to [3H]DAG, nor did it consistently affect the activities of phospholipase C or D. NGF did increase phospholipase A2 activity, however the hydrolysis catalyzed by this enzyme does not liberate DAG. Hence the major source of the increased DAG levels in PC12 cells exposed to NGF appears to be enhanced de novo DAG synthesis, probably initiated by the activation of LCASs, rather than the breakdown of PC or PI.

Using PC12 cells undergoing neurite outgrowth, we studied the activation of various fatty acids, of different chain lengths and degrees of saturation, by long chain acyl-CoA synthetases (LCASs). Cells treated with nerve growth factor (NGF) were labeled with [3H]glycerol, [3H]oleic acid (OA) or [3H]arachidonic acid (AA) in the presence of other unlabeled fatty acids of endogenous or exogenous origin. Triacsin C (4.8 μM), an inhibitor of acyl-CoA synthetase, decreased the incorporation of exogenous [3H]OA into glycerolipids by 30–90%, and increased by about 60% the accumulation of free [3H]OA in the cells. However it did not affect the incorporation of endogenous fatty acids nor of exogenous [3H]AA into phospholipids, suggesting that LCASs which activate exogenous AA and at least some endogenous fatty acids are relatively insensitive to this drug. Activities of the LCAS that is specific for AA (ACS), or of the non-specific LCAS which activates OA and other fatty acids (OCS), were much higher in microsomal and cytoplasmic fractions than in mitochondria or nuclei. The Vmax and Km values of ACS and OCS in microsomes were 12 and 0.7 nmol/min/mg protein and 70 and 37 μM, respectively; and in cytoplasm, 6 and 0.6 nmol/ min/mg protein and 38 and 60 μM, respectively. Triacsin C (2–33 μM) did not affect ACS activity in microsomal or cytoplasmal fractions, but inhibited OCS activities dose-dependently and competitively: IC50 and apparent Ki values were 13.5 μM and 14 μM in microsomes, and 3.8 μM and 4 μM in cytoplasm. NGF stimulated the activities of the LCASs, and, consistently, the incorporation of the various fatty acids into glycerolipids. These data indicate that LCASs are heterogeneous with respect to their intracellular locations, substrate specificities, kinetic characteristics and sensitivities to triacsin C; and that this heterogeneity affects the extents to which individual fatty acids are utilized to form glycerolipids.

Brain serotonin appears to be an excellent target for designing drugs to treat obesity. The prototype drug dexfenfluramine accelerates the onset of satiety and suppresses “carbohydrate craving,” the tendency to consume large quantities of snacks rich in carbohydrates and fats but not proteins. The drug works by blocking serotonin’s reuptake into presynaptic terminals; its metabolite norfenfluramine also releases serotonin into synapses and activates certain postsynaptic serotonin receptors. Dopaminergic drugs such as amphetamine and phentermine suppress the appetite but apparently lack macronutrient specificity. The special importance of serotoninergic neurons in feeding behavior derives in part from the fact that eating per se affects the production and release of serotonin. This is because dietary carbohydrates, acting via insulin—which lowers plasma concentrations of the large neutral amino acids (LNAA)—increase the uptake of tryptophan in the brain; this in turn increases the substrate saturation of tryptophan hydroxylase, the key enzyme that converts this amino acid to serotonin. Paradoxically, dietary proteins—which, unlike carbohydrates or fats, do contain tryptophan—decrease tryptophan’s uptake in the brain (because they cause disproportionately great increases in blood levels of the other LNAA, which compete with tryptophan for brain uptake), and thus fail to increase brain tryptophan or serotonin levels. Brain serotonin also is critically involved in controling mood, and many patients learn that they can improve their mood by eating carbohydrate-rich, protein-poor foods, particularly as snacks. This carbohydrate craving transiently ameliorates their depressive symptoms, but predisposes to weight gain, a phenomenon readily observed in people with seasonal affective disorder syndrome, premenstrual syndrome, or nicotine withdrawal.

Induction of neurite outgrowth by treating pheochromocytoma cells (PC12 cells) with nerve growth factor (NGF) is associated with major increases in cellular levels of diacylglycerol (DAG), an essential and probably limiting precursor in phosphatidylcholine (PC) and phosphatidylethanolamine (PE) syntheses. To identify the sources of this DAG we examined the effects of NGF treatment on the conversion of [3H]oleic acid (OA) or [3H]glycerol to [3H]glycerolipids, and the turnover of these products in PC12 cells. In kinetic studies on [3H]OA incorporation, most of the radioactivity in the cells initially was free [3H]OA; then it appeared predominantly as [3H]DAG and, eventually, as large amounts of [3H]phospholipids (PLs). In NGF pre-treated cells, the increases in the levels of [3H]DAG (which were most prominent) and PLs were similar to those in unlabeled DAG and PLs. These effects of NGF could be partially blocked by an inhibitor (triacsin C) of long chain acyl-CoA synthetase. NGF pre-treatment also significantly enhanced the incorporation of [3H]glycerol into lipids, a pathway for de novo synthesis of glycerolipids. In studies on the degradation of [3H]OA-labeled lipids, the disappearance of [3H]OA-labeled neutral lipids exhibited an initial rapid phase and a subsequent stable phase. NGF treatment transiently promoted the hydrolysis of [3H]PI to [3H]DAG. These data suggest that the increases in DAG levels observed in PC12 cells exposed to NGF derive mainly from de novo synthesis and, to a lesser and transient extent, from the hydrolysis of [3H]PI.

This study examines the range of serum melatonin concentrations that occur among young and older adults, and tests the effects of orally administered melatonin on the serum and saliva concentrations of the hormone. Healthy volunteers (20-36 per study), aged 20-73 years, were divided into two groups on the basis of age (29.2 +/- 6.5 and 60 +/- 8.8 years). For study 1: Serum melatonin levels were measured at 15 to 60 min intervals over a 25 h period using a radioimmunoassay. For study 2: serum and saliva melatonin levels were measured before and at intervals after the administration of a 0.3 mg dose of melatonin at 11.00 h. The younger subjects had significantly higher peak endogenous melatonin concentrations (+/- SD) and greater inter-individual variability (100.9 +/- 48.6 pg/ml) than the older subjects (34.5 +/- 15.4 pg/ml). Mean melatonin levels following treatment with the hormone tended to be higher and were significantly more variable among the group of older volunteers (254.5 +/- 145.7) than among the younger group (170.2 +/- 22.0 pg/ml). We conclude that although the peak endogenous serum melatonin levels are lower in elderly adults, the increment in serum melatonin levels induced by a low oral dose of the hormone is greater and more variable among people over 48 years old.

Phospholipids are the major constituents of cell membranes, and have numerous structural and functional roles in the nervous system. Although the metabolic pathways responsible for the syntheses of the phosphatides phosphatidylcholine (PtdCho), phosphatidylethanolamine (PtdEtn), and phosphatidylserine (PtdSer) are well understood, the mechanisms controlling these pathways in neural tissue have not been fully characterized. Recent studies have suggested that the main factors controlling PtdCho and PtdEtn synthesis by the Kennedy cycle tend to be the intracellular levels of key substrates for the biosynthetic enzymes, or changes in the activities of the rate-limiting enzymes. Moreover, different control mechanisms may operate, depending upon the functional state of the tissue.