Lipoprotein Particles in Cerebrospinal Fluid.

The brain is the most lipid-rich organ in the body, and the intricate interplay between lipid metabolism and pathologies associated with neurodegenerative disorders is being increasingly recognized. The brain is bathed in cerebrospinal fluid (CSF), which, like plasma, contains lipid-protein complexes called lipoproteins that are responsible for extracellular lipid transport. Multiple CSF lipoprotein populations exist, some of which are produced de novo in the central nervous system and others that appear to be generated from protein constituents that are produced in the periphery. These CSF lipoproteins are thought to play key roles in maintaining lipid homeostasis in the central nervous system, while little else is known due to their limited accessibility and their low abundance in CSF. Recent work has provided new insights into the compositional complexity of CSF lipoprotein families and their metabolism in cerebral circulation. The purpose of this review is to summarize our current state of knowledge on the composition, origin, and metabolism of CSF lipoproteins.

WNT5A is transported via lipoprotein particles in the cerebrospinal fluid to regulate hindbrain morphogenesis.

WNTs are lipid-modified proteins that control multiple functions in development and disease via short- and long-range signaling. However, it is unclear how these hydrophobic molecules spread over long distances in the mammalian brain. Here we show that WNT5A is produced by the choroid plexus (ChP) of the developing hindbrain, but not the telencephalon, in both mouse and human. Since the ChP produces and secretes the cerebrospinal fluid (CSF), we examine the presence of WNT5A in the CSF and find that it is associated with lipoprotein particles rather than exosomes. Moreover, since the CSF flows along the apical surface of hindbrain progenitors not expressing Wnt5a, we examined whether deletion of Wnt5a in the ChP controls their function and find that cerebellar morphogenesis is impaired. Our study thus identifies the CSF as a route and lipoprotein particles as a vehicle for long-range transport of biologically active WNT in the central nervous system.

Soluble LR11 competes with amyloid ß in binding to cerebrospinal fluid-high-density lipoprotein.

BACKGROUND: LR11 is a member of the low-density lipoprotein (LDL) receptor family with high expression in neurons. Some cell surface LR11 is cleaved and secreted into the cerebrospinal fluid (CSF) as soluble LR11 (sLR11). Patients with Alzheimer's disease (AD), particularly apolipoprotein E4 carriers, have high CSF-sLR11 and low CSF-amyloid ß (Aß) concentrations. Therefore, we assessed whether sLR11 is bound to CSF-high-density lipoprotein (HDL) and whether sLR11 competes with Aß in binding to apoE in CSF-HDL. METHODS: We measured CSF-sLR11 concentrations (50 controls and 16 patients with AD) using enzyme immunoassay. sLR11 and apoE distribution in the CSF was evaluated using non-denaturing two-dimensional gel electrophoresis (N-2DGE). ApoE bound to sLR11 or Aß was identified using co-immunoprecipitation assay. RESULTS: CSF-sLR11 concentrations were higher in patients with AD than controls (adjusted for sLR11 using phospholipid). N-2DGE analysis showed that sLR11 and Aß comigrated with a large apoE-containing CSF-HDL. Moreover, fewer apoE was bound to Aß when a higher amount of apoE was bound to sLR11 in patients with AD who presented with ε4/4. CONCLUSION: sLR11 binds to CSF-HDL and competes with Aß in binding to apoE in CSF-HDL, indicating that sLR11 affects Aß clearance via CSF-HDL.

[Lipoproteins and their receptors in the central nervous system].

Central nervous system(CNS) has nearly a quarter of total body cholesterol, although its weight is only 2% of the whole body. In the adult brain, cholesterol synthesis is extremely low, and a half life of cholesterol is about 5 years. In the cerebrospinal fluid(CSF), the only lipoprotein is high-density lipoprotein (HDL). CSF-HDL is larger than plasma HDL, and rich in apolipoprotein E (apoE). In CNS, neurons and glia cells express several lipoprotein receptors and ATP-binding cassette (ABC) transporters. These lipoprotein receptors can bind to and take up CSF-HDL for cholesterol recycling. Recent research has focused on investigating the role of CSF-HDL and lipoprotein receptors in the pathogenesis of Alzheimer disease.

A case of invasive central nervous system aspergillosis treated with micafungin with monitoring of micafungin concentrations in the cerebrospinal fluid.

Invasive aspergillosis has an extremely high mortality rate. In Japan, micafungin, an echinocandin drug that has a new mechanism of action as an antifungal agent and has a clinical effect against Aspergillus species, became available in 2002. However, little is known about its penetration into the central nervous system (CNS), or its efficacy for the treatment of invasive CNS aspergillosis. We report a 65-y-old female with diabetes mellitus and CNS aspergillosis who was treated with micafungin. During treatment, micafungin concentrations were measured in the cerebrospinal fluid and plasma. On a dose of 300 mg/d, the ratio of the micafungin concentration in the cerebrospinal fluid to that in plasma was extremely low (0.2%-0.05%); nevertheless, the patient did not have a relapse of invasive CNS aspergillosis after micafungin treatment.

Vitamin E in neurodegenerative disorders: Alzheimer's disease.

Oxidative stress is important in the pathogenesis of Alzheimer's disease (AD). The brain contains high levels of oxidizable lipids that must be protected by antioxidants. Low concentrations of vitamin E, quantitatively the major lipophilic antioxidant in the brain, are frequently observed in cerebrospinal fluid (CSF) of AD patients, suggesting that supplementation with vitamin E might delay the development of AD. In a placebo-controlled trial, vitamin E (2000 IU/day, 2 years) slowed (-53%) functional deterioration in patients with moderate AD (Sano et al., N. Engl. J. Med. 336: 1216-1222, 1997). Recently, use of vitamin E and vitamin C supplements in combination was found to be associated with reduced prevalence (-78%) and incidence (-64%) of AD in elderly population (Zandi et al., Arch. Neurol. 61: 82-88, 2004). These results are consistent with the ability of the supplementation with vitamin E (400 IU/day, 1 month) to increase its levels in CSF (123%) and plasma (145%) of AD patients and, in combination with vitamin C (1000 g/day), to decrease the susceptibility of CSF lipoproteins (up to -32%) to in vitro oxidation (Kontush et al., Free Radic. Biol. Med. 31: 345-354, 2001). In addition, vitamin E reduced lipid peroxidation and amyloid deposition in a transgenic mice model of AD (Sung et al., FASEB J. 18: 323-325, 2004). Computer modeling of the influence of vitamin E on lipoprotein oxidation reveals that the vitamin develops antioxidative activity in CSF lipoproteins in the presence of physiologically relevant, low amounts of oxidants. By contrast, under similar conditions, vitamin E behaves as a pro-oxidant in plasma lipoproteins, consistent with the model of tocopherol-mediated peroxidation (Stocker, Curr. Opin. Lipidol. 5: 422-433, 1994). This distinction is related to major differences in the levels of vitamin E (50 nM vs. 30 microM) and oxidizable lipids (4 microM vs. 2.5 mM) between CSF and plasma, which result in major differences in oxidative conditions (per unit of vitamin E) between CSF and plasma in the presence of similar amounts of oxidants. Altogether, these data suggest that vitamin E may be effective against in vivo oxidation of CSF lipoproteins and brain lipids, and offer new perspectives in the treatment of AD and other neurodegenerative disorders.

Remodelling of cerebrospinal fluid lipoproteins after subarachnoid hemorrhage.

Lipoprotein particles (Lps) in normal human cerebrospinal fluid (CSF) are distinct from those found in plasma and include unique apolipoprotein E (apoE indicates protein; APOE, gene) containing lipoproteins rarely seen in human plasma. Less favourable neurological recovery after subarachnoid hemorrhage (SAH) has been observed in patients who possess the APOE epsilon4 allele raising the possibility that apoE influences neuronal survival after brain injury. We analysed Lps from control and SAH CSF testing the hypotheses that following brain injury CSF Lps undergo remodelling and apoE containing Lps are selectively depleted from brain injury CSF. Lipoproteins were fractionated using CSF from six control pools and six patients with SAH on a sepharose 6HR 10/30 size exclusion column. Fractions were assayed for total cholesterol (TC), free cholesterol (FC), phospholipid, triglyceride (TG), apoE, apolipoprotein B (apoB), and apolipoprotein AI (apoAI). Compared to control CSF there were significant (P<0.05) increases in TC, FC, TG, and apoAI in SAH CSF. Plasma sized apoB-containing lipoproteins and a very small apoAI-containing Lps were identified in the SAH CSF, which were not present in controls. However, despite the release of plasma lipoproteins into the subarachnoid space, there was no significant increase in CSF apoE. These data provide novel indirect evidence suggesting that after SAH CSF Lps undergo remodelling and apoE containing Lps are selectively reduced in brain injury CSF. The remodelling of CSF Lps and selective reduction of apoE containing lipoproteins may reflect an important response of the human brain to injury.

Remodeling of cerebrospinal fluid lipoprotein particles after human traumatic brain injury.

The association between possession of the APOE epsilon4 allele and unfavourable outcome after traumatic brain injury (TBI) suggests that the apolipoprotein E protein (apoE) plays a key role in the response of the human brain to injury. ApoE is known to regulate cholesterol metabolism in the periphery through its action as a ligand for receptor mediated uptake of lipoprotein particles (Lps). Greater understanding of cholesterol metabolism in the human central nervous system may identify novel treatment strategies applicable to acute brain injury. We report findings from the analysis of lipoproteins in the cerebrospinal fluid (CSF) of patients with TBI and non-injured controls, testing the hypothesis that remodeling of CSF lipoproteins reflects the response of the brain to TBI. CSF Lps were isolated from the CSF of controls and patients with severe TBI by size exclusion chromatography, and the lipoprotein fractions analysed for cholesterol, phospholipid, apoAI, and apoE. There was a marked decrease in apoE containing Lps in the TBI CSF compared to controls (p=0.002). After TBI there was no significant decrease in apoAI containing CSF Lps (CSF LpAI), but the apoAI resided on smaller sized particles than in control CSF. There was a population of very small sized Lps in TBI CSF, which were associated with the increased cholesterol (p=0.0001) and phospholipid (p=0.040) seen after TBI. The dramatic loss of apoE containing Lps from the CSF, and the substantial increase in CSF cholesterol, support the concept that apoE and cholesterol metabolism are intimately linked in the context of acute brain injury. Treatment strategies targeting CNS lipid transport, required for neuronal sprouting and synaptogenesis, may be applicable to traumatic brain injury.

CSF lipoproteins and Alzheimer's disease.

Alterations in lipid homeostasis have been suggested to play a role in the pathogenesis of Alzheimer's disease (AD). This hypothesis is supported by the observed changes in lipid content and composition of AD brains when compared to age-matched control brains. The association between the e4 allele of the apolipoprotein E gene and increased risk of AD implicates lipoproteins in the pathogenesis. Lipoproteins are macromolecular particles responsible for lipid trafficking and metabolism. CNS lipoproteins are different from their plasma counter parts. We review the current understanding of the structure and functions of CNS lipoproteins. In addition to mediating lipid trafficking and metabolism, there is increasing evidence that apoE-containing lipoproteins are also involved in dendritic remodeling and synaptogensis and maintenance of the synapto-dendritic complexity during aging. Interestingly, these functions have been shown to be apoE-isoform specific with apoE4 lacking the activities of apoE3 and apoE2. In addition to the association between apoE4 and an increased risk of AD, oxidative stress is believed to play a role in the pathogenesis of this disease. Indeed evidence of lipid peroxidation in cerebral spinal fluid (CSF) lipoproteins from AD patients has been observed. Oxidation of lipoproteins not only eliminates their supportive roles in neurite outgrowth and synaptogenesis, but actually transforms them into neurotoxic agents. The elucidation of the pathways and mechanisms by which apoE-isoform and oxidation affect lipoprotein function in the CNS remains a challenge for scientist in the field of neurodegenerative disease.

Cerebrospinal fluid lipoprotein delivery to human neuronal cells is increased in Alzheimer's disease and is dependent on apoE monomer concentration.

Recent studies of cerebrospinal fluid (CSF) have shown increased oxidation of CSF lipoproteins in Alzheimer's disease (AD) patients, and neurotoxicity from oxidized CSF lipoproteins in culture. Since inheritance of different alleles of the apolipoprotein (apo) E gene is a risk factor for AD and apoE is the major lipoprotein trafficking molecule in brain, we hypothesized that apoE may modify the pathogenesis of AD by directing the delivery of oxidized CSF lipoproteins to neurons. To test this hypothesis, we adapted a method previously used with isolated plasma lipoproteins to specifically label lipid particles in situ in native CSF and quantified their delivery to human SK-N-BE(2)C neuroblastoma cells. CSF lipoproteins were delivered to neuronal cells largely through apoE-dependent processes. Importantly, CSF lipoproteins from AD patients were delivered more efficiently than CSF lipoproteins from age-matched controls; this effect was not associated with apoE genotype or degree of CSF lipoprotein oxidation but was associated with apoE monomer concentration that tended to be lower in AD patients. The inverse relationship between apoE monomer concentration and CSF lipoprotein delivery was duplicated in SK-N-BE(2)C cells, but not human astrocytoma cells, using artificial lipid particles and purified human apoE. These results suggest that lipoproteins in CSF from AD patients are delivered more efficiently to neurons than are CSF lipoproteins from controls, and that this abnormality may be explained largely by variations in CSF apoE concentration.

Characterization of four lipoprotein classes in human cerebrospinal fluid.

Lipoprotein metabolism in brain has not yet been fully elucidated, although there are a few reports concerning lipids in the brain and lipoproteins and apolipoproteins in the cerebrospinal fluid (CSF). To establish normal levels of lipoproteins in human CSF, total cholesterol, phospholipids, and fatty acids as well as apolipoprotein E (apoE) and apoA-I levels were determined in CSF samples from 216 individuals. For particle characterization, lipoproteins from human CSF were isolated by affinity chromatography and analyzed for size, lipid and apolipoprotein composition. Two consecutive immunoaffinity columns with antibodies, first against apoE and subsequently against apoA-I, were used to define four distinct lipoprotein classes. The major lipoprotein fraction consisted of particles of 13;-20 nm containing apoE and apoA-I as well as apoA-IV, apoD, apoH, and apoJ. In the second particle class (13;-18 nm) mainly apoA-I and apoA-II but no apoE was detected. Third, there was a small number of large particles (18;-22 nm) containing no apoA-I but apoE associated with apoA-IV, apoD, and apoJ. In the unbound fraction we detected small particles (10;-12 nm) with low lipid content containing apoA-IV, apoD, apoH, and apoJ. In summary, we established lipid and apolipoprotein levels in CSF in a large group of individuals and described four distinct lipoprotein classes in human CSF, differing in their apolipoprotein pattern, lipid composition, and size. On the basis of our own data and previous findings from other groups, we propose a classification of CSF lipoproteins.

Amyloid-beta is an antioxidant for lipoproteins in cerebrospinal fluid and plasma.

Amyloid-beta (Abeta) peptide, a major constituent of senile plaques and a hallmark of Alzheimer's disease (AD), is normally secreted by neurons and can be found in low concentrations in cerebrospinal fluid (CSF) and plasma, where it is associated with lipoproteins. However, the physiological role of Abeta secretion remains unknown. Here we show that at the concentrations measured in biological fluids (0.1-1.0 nM), Abeta(1-40) strongly inhibits autooxidation of CSF lipoproteins and plasma low density lipoprotein (LDL). At higher concentrations of the peptide its antioxidant action was abolished. Abeta(1-40) also inhibited copper-catalyzed LDL oxidation when added in molar excess of copper, but did not influence oxidation induced by an azo-initiator. Other Abeta peptides also possessed antioxidant activity in the order Abeta(1-40) > Abeta(1-42) > Abeta(25-35), whereas Abeta(35-25) was inactive. These data suggest that Abeta(1-40) may act as a physiological antioxidant in CSF and plasma lipoproteins, functioning by chelating transition metal ions.

Resistance of human cerebrospinal fluid to in vitro oxidation is directly related to its amyloid-beta content.

Amyloid-beta (A beta) peptide, a major constituent of senile plaques and a hallmark of Alzheimer's disease (AD), is normally secreted by neurons and can be found in low concentrations in cerebrospinal fluid (CSF) and plasma where it is associated with lipoproteins. However, the physiological role of A beta secretion remains unknown. We measured the resistance to in vitro oxidation of CSF obtained from 20 control subjects and 30 patients with AD, and correlated it with CSF levels of antioxidants, lipids and A beta. We found that the oxidative resistance, expressed as a duration of the oxidation lag-phase, was directly related to CSF levels of A beta 1-40, A beta 1-42 and ascorbate and inversely to levels of fatty acids. These data suggest that, besides ascorbate, A beta is another major physiological antioxidant for CSF lipoproteins.

Human, but not bovine, oxidized cerebral spinal fluid lipoproteins disrupt neuronal microtubules.

Cerebral spinal fluid (CSF) lipoproteins have become a focus of research since the observation that inheritance of particular alleles of the apolipoprotein E gene affects the risk of Alzheimer's disease (AD). There is evidence of increased lipid peroxidation in CSF lipoproteins from patients with AD, but the biological significance of this observation is not known. A characteristic of the AD brain is a disturbance of the neuronal microtubule organization. We have shown previously that 4-hydroxy-2(E)-nonenal, a major product of lipid peroxidation, causes disruption of neuronal microtubules and therefore tested whether oxidized CSF lipoproteins had the same effect. We exposed Neuro 2A cells to human CSF lipoproteins and analyzed the microtubule organization by immunofluorescence. In vitro oxidized human CSF lipoproteins caused disruption of the microtubule network, while their native (nonoxidized) counterparts did not. Microtubule disruption was observed after short exposures (1 h) and lipoprotein concentrations were present in CSF (20 microg/mL), conditions that did not result in loss of cell viability. Importantly, adult bovine CSF lipoproteins, oxidized under identical conditions, had no effect on the microtubule organization of Neuro 2A cells. Comparison of human and bovine CSF lipoproteins revealed similar oxidation-induced modifications of apolipoproteins E and A-I as analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting. Fatty acid analysis revealed substantially lower amounts of unsaturated fatty acids in bovine CSF lipoproteins, when compared to their human counterparts. Our data therefore indicate that oxidized human CSF lipoproteins are detrimental to neuronal microtubules. This effect is species-specific, since equally oxidized bovine CSF lipoproteins left the neuronal microtubule organization unchanged.

Cerebrospinal fluid lipoproteins in Alzheimer's disease.

Interest in cerebrospinal fluid (CSF) lipoproteins has been stimulated by the association of certain alleles of the human apolipoprotein E gene (APOE) with an increased risk of Alzheimer's disease (AD), and because apolipoprotein E (apoE) is one of the major apolipoproteins in CSF. CSF lipoproteins (d < 1.210 g/ml fraction) are distinct from their plasma counterparts, and in AD patients CSF may contain novel particles. The protein concentration of CSF lipoproteins is reduced in AD patients. Moreover, the molecular distribution of apoE- and apoAII-containing apolipoproteins in CSF is dictated by APOE. The lipid composition suggests that CSF lipoproteins from AD patients may have undergone increased free radical-mediated damage; experimental data support the possibility that this may occur both before and after lipoprotein assembly. Finally, human CSF lipoproteins oxidized ex vivo are neurotoxic to neuronal cells in culture and disrupt microtubule structure, an activity not observed with oxidized bovine CSF lipoproteins. CSF lipoproteins may represent a means whereby apoE influences the outcome of free radical-mediated damage to brain.

Differences in the Abeta40/Abeta42 ratio associated with cerebrospinal fluid lipoproteins as a function of apolipoprotein E genotype.

The epsilon4 allele of apolipoprotein E (ApoE) is a risk factor for Alzheimer's disease (AD). ApoE, which is important for lipid metabolism, is also a major constituent of cerebrospinal fluid (CSF) lipoproteins (LPs). Although ApoE in the CSF is derived from the central nervous system, the relation between LP metabolism in plasma and CSF is not clear. Soluble amyloid-beta (Abeta) protein may normally be associated with CSF LPs. It is converted in AD to a fibrillar form in brain parenchyma. ApoE and CSF LPs may regulate this process. The purpose of this study was to characterize CSF LPs from healthy, cognitively normal, fasted, elderly individuals at different risk for AD based on ApoE genotype. Lipid composition of CSF LPs did not differ with ApoE genotype. Interestingly, plasma and CSF high-density lipoprotein (HDL) cholesterol and apolipoprotein AI (ApoAI) levels were correlated. Importantly, as assessed by size-exclusion chromatography, Abeta in CSF coeluted in fractions containing LPs and was influenced by ApoE genotype: E4-positive subjects displayed significant elevations in Abeta40/Abeta42 ratios. These results suggest that plasma ApoAI/HDL levels can influence CSF ApoAI/HDL levels and that interactions between Abeta and central nervous system LPs may reflect changes in brain Abeta metabolism before the onset of clinical disease.

Lipoproteins in the central nervous system.

Although the synthesis and metabolism of plasma lipoproteins are well characterized, little is known about lipid delivery and clearance within the central nervous system (CNS). Our work has focused on characterizing the lipoprotein particles present in the cerebrospinal fluid (CSF) and the nascent particles secreted by astrocytes. In addition to carrying lipids, we have found that beta-amyloid (A beta) associates with lipoproteins, including the discoidal particles secreted by cultured astrocytes and the spherical lipoproteins found in CSF. We believe that association with lipoproteins provides a means of transport and clearance for A beta. This process may be further influenced by an interaction between A beta and apoprotein E (apoE), the primary protein component of CNS lipoproteins. Specifically, we have investigated the formation and physiologic relevance of a SDS-stable complex between apoE and A beta. In biochemical assays, native apoE2 and E3 (associated with lipid particles) form an SDS-stable complex with A beta that is 20-fold more abundant than the apoE4:A beta complex. In cell culture, native apoE3 but not E4 prevents A beta-induced neurotoxicity by a mechanism dependent on cell surface apoE receptors. In addition, apoE and the inhibition of apoE receptors prevent A beta-induced astrocyte activation. Therefore, we hypothesize that the protection from A beta-induced neurotoxicity afforded by apoE3 may result from clearance of the peptide by SDS-stable apoE3:A beta complex formation and uptake by apoE receptors.

Characterization and functional studies of lipoproteins, lipid transfer proteins, and lecithin:cholesterol acyltransferase in CSF of normal individuals and patients with Alzheimer's disease.

We investigated the lipoprotein distribution and composition in cerebrospinal fluid (CSF) in a group of patients with Alzheimer's disease (AD) or affected by other types of dementia in comparison to non-demented controls. We found slightly decreased apolipoprotein (apo)E and cholesterol concentrations in CSF of AD patients and moderately increased apoA-I concentrations, while in patients suffering from other types of dementia the apoA-I CSF concentration was increased. ApoA-IV concentrations varied widely in human CSF, but were not associated with any clinical condition. HDL(2)-like apoE-containing lipoproteins represent the major lipoprotein fraction. In CSF of normal controls, only a minor HDL(3)-like apoA-I-containing lipoprotein fraction was observed; this fraction was more prevalent in AD patients. ApoA-II was recovered mostly in the HDL(3) density range, while apoA-IV was not associated with lipoproteins but appeared in a lipid-free form, co-localizing with LCAT immunoreactivity. Bi-dimensional analysis demonstrated pre-beta and alpha apoA-I-containing particles; apoE and apoA-II were detected only in alpha-migrating particles. ApoA-IV distributed both to pre-beta and gamma-migrating particles; the LCAT signal was co-localized in this gamma-migrating fraction. Enzymatically active LCAT was present in human CSF as well as PLTP activity and mass; no CETP mass was detected. In CSF from AD patients, LCAT activity was 50% lower than in CSF from normal controls. CSF lipoproteins induced a significant cholesterol efflux from cultured rat astrocytes, suggesting that they play an active role in maintaining the cholesterol homeostasis in brain cells.

Increased lipoprotein oxidation in Alzheimer's disease.

Oxidation has been proposed to be an important factor in the pathogenesis of Alzheimer's disease (AD) and amyloid beta is considered to induce oxidation. In biological fluids, including cerebrospinal fluid (CSF), amyloid beta is found complexed to lipoproteins. On the basis of these observations, we investigated the potential role of lipoprotein oxidation in the pathology of AD. Lipoprotein oxidizability was measured in vitro in CSF and plasma from 29 AD patients and found to be significantly increased in comparison to 29 nondemented controls. The levels of the hydrophilic antioxidant ascorbate were significantly lower in CSF and plasma from AD patients. In plasma, alpha-carotene was significantly lower in AD patients compared to controls while alpha-tocopherol levels were indistinguishable between patients and controls. In CSF, a nonsignificant trend to lower alpha-tocopherol levels among AD patients was found. Polyunsaturated fatty acids, the lipid substrate for oxidation, were significantly lower in the CSF of AD patients. Our findings suggest that (i) lipoprotein oxidation may be important in the development of AD and (ii) the in vitro measurement of lipid peroxidation in CSF might become a useful additional marker for diagnosis of AD.

Time-course of oxidation of lipids in human cerebrospinal fluid in vitro.

Oxidative mechanisms play an important role in the pathogenesis of Alzheimer's disease, Parkinson's disease and other neurodegenerative diseases. To assess whether the oxidation of brain lipoproteins plays a role in the development of these pathologies, we investigated whether the lipoproteins of human cerebrospinal fluid (CSF) are susceptible to oxidative modification in vitro. We studied oxidation time-course for up to 100 h of human CSF in the absence (autooxidation) or presence of exogenous oxidants. Autooxidation of diluted CSF was found to result in a slow accumulation of lipid peroxidation products. The time-course of lipid hydroperoxide accumulation revealed three consecutive phases, lag-phase, propagation phase and plateau phase. Qualitatively similar time-course has been typically found in human plasma and plasma lipoproteins. Autooxidation of CSF was accelerated by adding exogenous oxidants, delayed by adding antioxidants and completely inhibited by adding a chelator of transition metal ions. Autooxidation of CSF also resulted in the consumption of endogenous ascorbate, alpha-tocopherol, urate and linoleic and arachidonic acids. Taking into account that (i) lipid peroxidation products measured in our study are known to be derived from fatty acids, and (ii) lipophilic antioxidants and fatty acids present in CSF are likely to be located in CSF lipoproteins, we conclude that lipoproteins of human CSF are modified in vitro during its autooxidation. This autooxidation appears to be catalyzed by transition metal ions, such as Cu(II) and Fe(III), which are present in native CSF. These data suggest that the oxidation of CSF lipoproteins might occur in vivo and play a role in the pathogenesis of neurodegenerative diseases.