Concentrations of the water-soluble vitamins thiamin, ascorbic acid, and folic acid in serum and cerebrospinal fluid of healthy individuals

Nutritional metabolism and cerebral bioenergetics in Alzheimer's disease and related dementias

Disturbances in the brain's capacity to meet its energy demand increase the risk of synaptic loss, neurodegeneration, and cognitive decline. Nutritional and metabolic interventions that target metabolic pathways combined with diagnostics to identify deficits in cerebral bioenergetics may therefore offer novel therapeutic potential for Alzheimer's disease (AD) prevention and management. Many diet-derived natural bioactive components can govern cellular energy metabolism but their effects on brain aging are not clear. This review examines how nutritional metabolism can regulate brain bioenergetics and mitigate AD risk. We focus on leading mechanisms of cerebral bioenergetic breakdown in the aging brain at the cellular level, as well as the putative causes and consequences of disturbed bioenergetics, particularly at the blood-brain barrier with implications for nutrient brain delivery and nutritional interventions. Novel therapeutic nutrition approaches including diet patterns are provided, integrating studies of the gut microbiome, neuroimaging, and other biomarkers to guide future personalized nutritional interventions.

Ascorbate content of clinical glioma tissues is related to tumour grade and to global levels of 5-hydroxymethyl cytosine

Gliomas are incurable brain cancers with poor prognosis, with epigenetic dysregulation being a distinctive feature. 5-hydroxymethylcytosine (5-hmC), an intermediate generated in the demethylation of 5-methylcytosine, is present at reduced levels in glioma tissue compared with normal brain, and that higher levels of 5-hmC are associated with improved patient survival. DNA demethylation is enzymatically driven by the ten–eleven translocation (TET) dioxygenases that require ascorbate as an essential cofactor. There is limited data on ascorbate in gliomas and the relationship between ascorbate and 5-hmC in gliomas has never been reported. Clinical glioma samples (11 low-grade, 26 high-grade) were analysed for ascorbate, global DNA methylation and hydroxymethylation, and methylation status of the O-6-methylguanine-DNA methyltransferase (MGMT) promoter. Low-grade gliomas contained significantly higher levels of ascorbate than high-grade gliomas (p = 0.026). Levels of 5-hmC were significantly higher in low-grade than high-grade glioma (p = 0.0013). There was a strong association between higher ascorbate and higher 5-hmC (p = 0.004). Gliomas with unmethylated and methylated MGMT promoters had similar ascorbate levels (p = 0.96). One mechanism by which epigenetic modifications could occur is through ascorbate-mediated optimisation of TET activity in gliomas. These findings open the door to clinical intervention trials in patients with glioma to provide both mechanistic information and potential avenues for adjuvant ascorbate therapy.

The Contribution of Plasma and Brain Vitamin C on Age and Gender-Related Cognitive Differences: A Mini-Review of the Literature

There is increasing evidence that sex differences in the brain may contribute to gender-related behavioral differences, including cognitive function. Literature has revealed gender dimorphisms in cognitive function between males and females. Additionally, several risk factors associated with cognitive decline depend on chronological age. It is well recognized that the process of aging is associated with a decline in cognitive ability and brain function. Various explanations may account for these gender-related cognitive differences and age-associated cognitive changes. Recent investigations have highlighted the importance of vitamin C in maintaining brain health and its association with cognitive function in both cognitively intact and impaired cohorts. The present review explores previous literature that has evaluated differences in plasma/brain vitamin C between genders and during aging. It then assesses whether these age and gender-related differences may affect the relationship between plasma/brain vitamin C and cognition. The purpose of this review was to examine the evidence for a link between plasma/brain vitamin C and cognition and the impact of gender and age on this relationship. Epidemiological studies have frequently shown higher vitamin C plasma concentrations in women. Similarly, aging has been systematically associated with reductions in plasma vitamin C levels. A range of animal studies has demonstrated potential gender and age-related differences in vitamin C brain distribution and utilization. The reviewed literature suggests that gender differences in plasma and brain vitamin C may potentially contribute to differences in gender-associated cognitive ability, particularly while females are pre-menopausal. Additionally, we can propose that age-associated differences in plasma and brain vitamin C may be potentially linked to age-associated cognitive differences, with older cohorts appearing more vulnerable to experience declines in plasma vitamin C concentrations alongside compromised vitamin C brain regulation. This review encourages future investigations to take into account both gender and age when assessing the link between plasma vitamin C concentrations and cognitive function. Further large scale investigations are required to assess whether differences in cognitive function between genders and age groups may be causally attributed to plasma vitamin C status and brain distribution and utilization.

Influence of Bone Marrow-Derived Mesenchymal Stem Cell Therapy on Oxidative Stress Intensity in Minimally Conscious State Patients

Neurological disorders, including minimally conscious state (MCS), may be associated with the presence of high concentrations of reactive oxygen species within the central nervous system. Regarding the documented role of mesenchymal stem cells (MSCs) in oxidative stress neutralization, the aim of this study is to evaluate the effect of bone marrow-derived MSC (BM-MSC) transplantation on selected markers of oxidative stress in MCS patients. Antioxidant capacity was measured in cerebrospinal fluid (CSF) and plasma collected from nine patients aged between 19 and 45 years, remaining in MCS for 3 to 14 months. Total antioxidant capacity, ascorbic acid and ascorbate concentrations, superoxide dismutase, catalase, and peroxidase activity were analyzed and the presence of tested antioxidants in the CSF and plasma was confirmed. Higher ascorbic acid (AA) content and catalase (CAT) activity were noted in CSF relative to plasma, whereas superoxide dismutase (SOD) activity and total antioxidant capacity were higher in plasma relative to CSF. Total antioxidant capacity measured in CSF was greater after BM-MSC transplantations. The content of ascorbates was lower and CAT activity was higher both in CSF and plasma after the administration of BM-MSC. The above results suggest that MSCs modulate oxidative stress intensity in MCS patients, mainly via ascorbates and CAT activity.

Increased levels of ascorbic acid in the cerebrospinal fluid of cognitively intact elderly patients with major depression: a preliminary study

Major depressive disorder (MDD) in the elderly is a risk factor for dementia, but the precise biological basis remains unknown, hampering the search for novel biomarkers and treatments. In this study, we performed metabolomics analysis of cerebrospinal fluid (CSF) from cognitively intact elderly patients (N = 28) with MDD and age- and gender-matched healthy controls (N = 18). The CSF levels of 177 substances were measured, while 288 substances were below the detection limit. Only ascorbic acid was significantly different, with higher levels in the MDD group at baseline. There were no correlations between CSF ascorbic acid levels and clinical variables in MDD patients at baseline. At the 3-year follow-up, there was no difference of CSF ascorbic acid levels between the two groups. There was a negative correlation between CSF ascorbic acid and CSF amyloid-β₄₂ levels in all subjects. However, there were no correlations between ascorbic acid and other biomarkers (e.g., amyloid-β₄₀, total and phosphorylated tau protein). This preliminary study suggests that abnormalities in the transport and/or release of ascorbic acid might play a role in the pathogenesis of late-life depression.

Evaluation of carbon nanotube fiber microelectrodes for neurotransmitter detection: Correlation of electrochemical performance and surface properties

Fibers made of CNTs are attractive microelectrode sensors because they can be directly fabricated into microelectrodes. Different protocols for making CNT fibers have been developed, but differences in surface structure and therefore electrochemical properties that result have not been studied. In this study, we correlated the surface and electrochemical properties for neurochemical detection at 3 types of materials: CNT fibers produced by wet spinning with (1) polyethylenimine (PEI/CNT) or (2) chlorosulfonic acid (CA/CNT), and (3) CNT yarns made by solid-based CNT drawing. CNT yarns had well-aligned, high purity CNTs, abundant oxygen functional groups, and moderate surface roughness which led to the highest dopamine current density (290 ± 65 pA/cm²) and fastest electron transfer kinetics. The crevices of the CNT yarn and PEI/CNT fiber microelectrodes allow dopamine to be momentarily trapped during fast-scan cyclic voltammetry detection, leading to thin-layer cell conditions and a response that was independent of applied waveform frequency. The larger crevices on the PEI/CNT fibers led to a slower time response, showing too much roughness is detrimental to fast detection. CA/CNT fibers have a smoother surface and lower currents, but their negative surface charge results in high selectivity for dopamine over uric acid or ascorbic acid. Overall, small crevices, high conductivity, and abundant oxygen groups led to high sensitivity for amine neurotransmitters, such as dopamine and serotonin. Thus, different surfaces of CNT fibers result in altered electrochemical properties and could be used in the future to predict and control electrochemical performance.

Electrochemical Detection of Dopamine via Assisted Ion Transfer at Nanopipet Electrode Using Cyclic Voltammetry

We present here the detection of dopamine (DA) at nanopipet electrodes with radii of hundreds of nanometers ranging from 160 nm to 480 nm. Dibenzo-18-crown-6 (DB18C6) was employed as an ionophore to facilitate DA transfer, resulting in a half-wave transfer potential, E1/2, DA, of -0.322 (±0.020) V vs. E1/2, TBA. Well-defined steady-state sigmoidal cyclic voltammograms were observed for the transfer of DA. High resolution scanning electron microscopy was used to measure the size and taper angle of the nanopipet electrodes. The detection is linear with concentration of DA ranging from 0.25 mM to 2 mM; calculated diffusion coefficient at nanopipet electrodes with above mentioned sizes is 4.87 (±0.28) × 10-10 m2/s. The effect of the common interferent ascorbic acid on DA detection with nanopipet electrodes was evaluated, where DA detection still shows linear behavior with well-defined sigmoidal CVs with E1/2, DA being -0.328 (±0.029) V vs. E1/2, TBA. The diffusion coefficient for DA transfer in MgCl2 with the presence of 2 mM AA was measured to be 1.93 (±0.59) × 10-10 m2/s on nanoelectrodes with radii from 161 nm to 263 nm, but the physiological concentration of 0.1 mM AA had no effect on DA's diffusion coefficient.

Recent trends in carbon nanomaterial-based electrochemical sensors for biomolecules: A review

Carbon nanomaterials are advantageous for electrochemical sensors because they increase the electroactive surface area, enhance electron transfer, and promote adsorption of molecules. Carbon nanotubes (CNTs) have been incorporated into electrochemical sensors for biomolecules and strategies have included the traditional dip coating and drop casting methods, direct growth of CNTs on electrodes and the use of CNT fibers and yarns made exclusively of CNTs. Recent research has also focused on utilizing many new types of carbon nanomaterials beyond CNTs. Forms of graphene are now increasingly popular for sensors including reduced graphene oxide, carbon nanohorns, graphene nanofoams, graphene nanorods, and graphene nanoflowers. In this review, we compare different carbon nanomaterial strategies for creating electrochemical sensors for biomolecules. Analytes covered include neurotransmitters and neurochemicals, such as dopamine, ascorbic acid, and serotonin; hydrogen peroxide; proteins, such as biomarkers; and DNA. The review also addresses enzyme-based electrodes that are used to detect non-electroactive species such as glucose, alcohols, and proteins. Finally, we analyze some of the future directions for the field, pointing out gaps in fundamental understanding of electron transfer to carbon nanomaterials and the need for more practical implementation of sensors.

Distribution of vitamin C is tissue specific with early saturation of the brain and adrenal glands following differential oral dose regimens in guinea pigs

Vitamin C (VitC) deficiency is surprisingly common in humans even in developed parts of the world. The micronutrient has several established functions in the brain; however, the consequences of its deficiency are not well characterised. To elucidate the effects of VitC deficiency on the brain, increased knowledge about the distribution of VitC to the brain and within different brain regions after varying dietary concentrations is needed. In the present study, guinea pigs (like humans lacking the ability to synthesise VitC) were randomly divided into six groups (n 10) that received different concentrations of VitC ranging from 100 to 1500 mg/kg feed for 8 weeks, after which VitC concentrations in biological fluids and tissues were measured using HPLC. The distribution of VitC was found to be dynamic and dependent on dietary availability. Brain saturation was region specific, occurred at low dietary doses, and the dose-concentration relationship could be approximated with a three-parameter Hill equation. The correlation between plasma and brain concentrations of VitC was moderate compared with other organs, and during non-scorbutic VitC deficiency, the brain was able to maintain concentrations from about one-quarter to half of sufficient levels depending on the region, whereas concentrations in other tissues decreased to one-sixth or less. The adrenal glands have similar characteristics to the brain. The observed distribution kinetics with a low dietary dose needed for saturation and exceptional retention ability suggest that the brain and adrenal glands are high priority tissues with regard to the distribution of VitC.

Levodopa: effect on cell death and the natural history of Parkinson's disease

This review article considers the question of whether or not levodopa is toxic in Parkinson's disease (PD). l-dopa is the most effective symptomatic treatment for PD and has provided benefit for millions of patients. However, there has been a longstanding concern that l-dopa might be toxic and accelerate neuronal degeneration and clinical progression as a consequence of reactive oxygen species generated by the drug's oxidative metabolism. In vitro, l-dopa can induce degeneration of dopaminergic neurons, but it is not clear that the effects of the drug on cultured dopamine neurons reflect what happens in the PD brain. In vivo, l-dopa has not been demonstrated to have toxic effects on dopamine neurons in normal, dopamine-lesioned, or oxidatively stressed animal models, but none of these models precisely replicates the PD condition. Clinical trials have tested the effect of l-dopa on clinical progression and have not demonstrated any findings indicative of toxicity. However, the symptomatic and long-duration effects of the drug could mask ongoing neuronal degeneration. Furthermore, l-dopa induces a greater decline in imaging measures of dopaminergic function than placebo or dopamine agonists, consistent with toxicity. Pathological studies have not demonstrated evidence of accelerated loss of dopamine neurons, but prospective and properly controlled studies with stereological unbiased counting have not been performed. Thus, although there is no hard evidence to suggest that l-dopa is toxic in PD patients, the issue has not been fully resolved. It is generally recommended that physicians continue to use l-dopa, but in the lowest dose that provides satisfactory clinical control.

The 1H NMR profile of healthy dog cerebrospinal fluid

The availability of data for reference values in cerebrospinal fluid for healthy humans is limited due to obvious practical and ethical issues. The variability of reported values for metabolites in human cerebrospinal fluid is quite large. Dogs present great similarities with humans, including in cases of central nervous system pathologies. The paper presents the first study on healthy dog cerebrospinal fluid metabolomic profile using ¹H NMR spectroscopy. A number of 13 metabolites have been identified and quantified from cerebrospinal fluid collected from a group of 10 mix breed healthy dogs. The biological variability as resulting from the relative standard deviation of the physiological concentrations of the identified metabolites had a mean of 18.20% (range between 9.3% and 44.8%). The reported concentrations for metabolites may be used as normal reference values. The homogeneity of the obtained results and the low biologic variability show that the ¹H NMR analysis of the dog’s cerebrospinal fluid is reliable in designing and interpreting clinical and therapeutic trials in dogs with central nervous system pathologies.

Expression Profiling of Solute Carrier Gene Families at the Blood-CSF Barrier

The choroid plexus (CP) is a highly vascularized tissue in the brain ventricles and acts as the blood-cerebrospinal fluid (CSF) barrier (BCSFB). A main function of the CP is to secrete CSF, which is accomplished by active transport of small ions and water from the blood side to the CSF side. The CP also supplies the brain with certain nutrients, hormones, and metal ions, while removing metabolites and xenobiotics from the CSF. Numerous membrane transporters are expressed in the CP in order to facilitate the solute exchange between the blood and the CSF. The solute carrier (SLC) superfamily represents a major class of transporters in the CP that constitutes the molecular mechanisms for CP function. Recently, we systematically and quantitatively examined Slc gene expression in 20 anatomically comprehensive brain areas in the adult mouse brain using high-quality in situ hybridization data generated by the Allen Brain Atlas. Here we focus our analysis on Slc gene expression at the BCSFB using previously obtained data. Of the 252 Slc genes present in the mouse brain, 202 Slc genes were found at detectable levels in the CP. Unsupervised hierarchical cluster analysis showed that the CP Slc gene expression pattern is substantially different from the other 19 analyzed brain regions. The majority of the Slc genes in the CP are expressed at low to moderate levels, whereas 28 Slc genes are present in the CP at the highest levels. These highly expressed Slc genes encode transporters involved in CSF secretion, energy production, and transport of nutrients, hormones, neurotransmitters, sulfate, and metal ions. In this review, the functional characteristics and potential importance of these Slc transporters in the CP are discussed, with particular emphasis on their localization and physiological functions at the BCSFB.

Thiamine diphosphate in whole blood, thiamine and thiamine monophosphate in breast-milk in a refugee population

BACKGROUND

The provision of high doses of thiamine may prevent thiamine deficiency in the post-partum period of displaced persons.

METHODOLOGY/PRINCIPAL FINDINGS

The study aimed to evaluate a supplementation regimen of thiamine mononitrate (100 mg daily) at the antenatal clinics in Maela refugee camp. Women were enrolled during antenatal care and followed after delivery. Samples were collected at 12 weeks post partum. Thiamine diphosphate (TDP) in whole blood and thiamine in breast-milk of 636 lactating women were measured. Thiamine in breast-milk consisted of thiamine monophosphate (TMP) in addition to thiamine, with a mean TMP to total thiamine ratio of 63%. Mean whole blood TDP (130 nmol/L) and total thiamine in breast-milk (755 nmol/L) were within the upper range reported for well-nourished women. The prevalence of women with low whole blood TDP (<65 nmol/L) was 5% and with deficient breast-milk total thiamine (<300 nmol/L) was 4%. Whole blood TDP predicted both breast-milk thiamine and TMP (R(2) = 0.36 and 0.10, p<0.001). A ratio of TMP to total thiamine ≥63% was associated with a 7.5 and 4-fold higher risk of low whole blood TDP and deficient total breast-milk thiamine, respectively. Routine provision of daily 100 mg of thiamine mononitrate post-partum compared to the previous weekly 10 mg of thiamine hydrochloride resulted in significantly higher total thiamine in breast-milk.

CONCLUSIONS/SIGNIFICANCE

Thiamine supplementation for lactating women in Maela refugee camp is effective and should be continued. TMP and its ratio to total thiamine in breast-milk, reported for the first time in this study, provided useful information on thiamine status and should be included in future studies of breast-milk thiamine.

Ascorbic acid, cognitive function, and Alzheimer's disease: a current review and future direction

This narrative review appraises the human and animal studies implicating ascorbic acid (AA) in normal cognitive function and Alzheimer's disease. A research framework for how nutrition affects brain aging is proposed with emphasis on AA intake, status, metabolism, and transport into brain tissue. A final synopsis highlights areas for future research regarding AA nourishment and healthy brain aging.

Plasma vitamin C is lower in postherpetic neuralgia patients and administration of vitamin C reduces spontaneous pain but not brush-evoked pain

OBJECTIVES

Plasma vitamin C concentrations have been suggested to be related to pain modulation in postherpetic neuralgia (PHN), an intractable neuropathic pain syndrome. In this study, we first compared plasma concentrations of vitamin C between healthy volunteers and PHN patients and then designed a symptom-based and mechanism-based approach to assess the analgesic effect of intravenous vitamin C on spontaneous and brush-evoked pain.

METHODS

Study 1 was cross-sectional that enrolled 39 healthy volunteers and 38 PHN patients. Study 2 was a double-blinded, placebo-controlled intervention study, which comprised 41 patients randomly allocated into the ascorbate group and placebo. Each patient received normal saline infusion with or without ascorbate on days 1, 3, and 5 and answered questionnaires that included side effects; numeric rating pain scale (NRS) on spontaneous and brush-evoked pain on days 1, 3, 5, and 7; and patient global impression of change on spontaneous and brush-evoked pain on day 7.

RESULTS

Study 1 revealed that plasma concentrations of vitamin C were significantly lower in patients with PHN than in healthy volunteers (P<0.001). Study 2 showed that ascorbate treatment effectively restored plasma vitamin C concentrations in the patients and decreased spontaneous pain by 3.1 in NRS from baseline to day 7, as compared with a decrease of 0.85 in NRS by placebo treatment (P<0.001). Conversely, ascorbate treatment did not significantly affect brush-evoked pain. Ascorbate treatment also resulted in a better efficacy than placebo in patient global impression of change on spontaneous pain (P<0.001) on day 7 and did not affect brush-evoked pain. No side effects were observed.

CONCLUSIONS

Plasma vitamin C status plays a role in PHN, and intravenous ascorbate helps relieve spontaneous pain in PHN.

Selective electrochemical sensor for folic acid at physiological pH using ultrathin electropolymerized film of functionalized thiadiazole modified glassy carbon electrode

This paper demonstrated the selective determination of folic acid (FA) in the presence of important physiological interferents, ascorbic acid (AA) and uric acid (UA) at physiological pH using electropolymerized film of 5-amino-2-mercapto-1,3,4-thiadiazole (p-AMT) modified glassy carbon (GC) electrode. Bare GC electrode fails to determine the concentration of FA in the presence of AA and UA due to the surface fouling caused by the oxidized products of AA and FA. However, the p-AMT film modified electrode not only separates the voltammetric signals of AA, UA and FA with potential differences of 170 and 410 mV between AA-UA and UA-FA, respectively but also shows higher oxidation current for these analytes. The p-AMT film modified electrode displays an excellent selectivity towards the determination of FA even in the presence of 200-fold AA and 100-fold UA. Using amperometric method, we achieved the lowest detection of 75 nM UA and 100 nM each AA and FA. The amperometric current response was increased linearly with increasing FA concentration in the range of 1.0 x 10(-7)-8.0 x 10(-4)M and the detection limit was found to be 2.3 x 10(-10)M (S/N=3). The practical application of the present modified electrode was successfully demonstrated by determining the concentration of FA in human blood serum samples.

CSF/serum folate gradient: physiology and determinants with special reference to dementia

BACKGROUND

Folate depletion has been implicated as a risk factor for neurodegenerative disorders. We hypothesized that transport of folate to the cerebrospinal fluid (CSF) compartment could be involved in the pathophysiology of these disorders.

METHODS

The CSF/serum folate gradient (R(CSF/S)) was studied in 205 subjects with suspected cognitive disorder. Its relation to clinical and biochemical indices, including the integrity of the blood-CSF barrier, were characterized.

RESULTS

In subjects who were diagnosed as nondemented (ND) the mean R(CSF/S )+/- SD was 2.46 +/- 0.62 versus 2.09 +/- 0.67 (p = 0.008) in the dementia subgroup with a vascular component (VaD + mixed). The ND subgroup had higher CSF folate (p = 0.001) and lower serum homocysteine values (p = 0.001) than the VaD + mixed subgroup. The folate gradient R(CSF/S) was negatively correlated with serum folate (p < 0.001, R(2) = 0.518) and to the albumin ratio, a blood-CSF barrier biomarker (beta = -0.235). The Alzheimer patients had R(CSF/S) and albumin ratios similar to the ND subjects.

CONCLUSION

The R(CSF/S) was significantly lower in the VaD + mixed dementia subgroup, suggestive of a defect in the transport of folate over the choroid plexus that seems to be characteristic of, and limited to, the VaD + mixed dementia subgroup.

Loop diuretic therapy, thiamine balance, and heart failure

Thiamine, or vitamin B1, is a water-soluble B complex vitamin that was first discovered in 1910 in the process of exploring how rice bran cured patients of beriberi. Thiamine is not synthesized in humans, therefore its availability for necessary cellular processes hinges on its continual ingestion. The amount of thiamine one needs to ingest to maintain balance is disease state-dependent or medication-dependent. Severe chronic thiamine deficiency can have significant neurologic and cardiac effects, the latter is reflected in a particular type of heart failure called wet beriberi. This form of heart failure clearly benefits from thiamine supplementation. It is unclear, however, whether thiamine supplementation offers any benefit in other forms of heart failure. Despite this, it is not unreasonable for heart failure patients to routinely ingest a thiamine-containing multivitamin; patients using diuretics have an increased urinary excretion of thiamine and thus are at a higher risk for developing thiamine deficiency. The role of thiamine in heart failure, however, remains arguable.

Levodopa in the treatment of Parkinson's disease: Current controversies

Levodopa is the most effective symptomatic agent in the treatment of Parkinson's disease (PD) and the "gold standard" against which new agents must be compared. However, there remain two areas of controversy: (1) whether levodopa is toxic, and (2) whether levodopa directly causes motor complications. Levodopa is toxic to cultured dopamine neurons, and this may be a problem in PD where there is evidence of oxidative stress in the nigra. However, there is little firm evidence to suggest that levodopa is toxic in vivo or in PD. Clinical trials have not clarified this situation. Levodopa is also associated with motor complications. Increasing evidence suggests that they are related, at least in part, to the short half-life of the drug (and its potential to induce pulsatile stimulation of dopamine receptors) rather than to specific properties of the molecule. Treatment strategies that provide more continuous stimulation of dopamine receptors provide reduced motor complications in MPTP monkeys and PD patients. These studies raise the possibility that more continuous and physiological delivery of levodopa might reduce the risk of motor complications. Clinical trials to test this hypothesis are underway. We review current evidence relating to these areas of controversy.

Functional characterisation of the active ascorbic acid transport into cerebrospinal fluid using primary cultured choroid plexus cells

Crossing the blood-CSF barrier is an important pathway for certain nutrients to enter the CNS. Cultured choroid plexus epithelial cells are a potent model system to study active transport properties of this tissue in vitro. In the present study this in vitro model was used to analyse ascorbic acid transport across the blood-CSF barrier that is supposedly mediated by the Na(+)-dependent transporter SVCT2. The expression of SVCT2 in the cultured cells was proven by RT-PCR. Active transport across the cell monolayer resulted in ascorbic acid enrichment at the CSF mimicking side. Ascorbic acid transport and uptake were decreased to 13 and 27%, respectively, in the presence of 200 microM phloretin. Inhibition of both transepithelial substrate transport (to 7.5%) and cytoplasmatic uptake (to 20%) was observed in Na(+)-free medium indicating that a basolaterally located and Na(+)-dependent transporter mediates ascorbic acid uptake. Substituting Cl(-) by either iodide or D-gluconate increased ascorbic acid uptake by factors of 3.7 or 2.5, respectively. Similar observations were made when Na(+)-dependent myo-inositol transport was analysed. Additionally, in presence of 100 microM bumetanide, an inhibitor of Na(+)-Cl(-)-cotransport, indirectly increased ascorbic acid and myo-inositol transport rates were observed showing that ascorbic acid-Na(+)-cotransport might balance low intracellular Na(+) concentration.

Rescue of hypercholesterolemia-related impairment of angiogenesis by oral folate supplementation

OBJECTIVES

We examined whether oral folate supplementation would rescue a hypercholesterolemia (HC)-related impairment of ischemia-induced angiogenesis.

BACKGROUND

Folate protects against endothelial dysfunction, but the effect of folate supplementation on angiogenesis is little known.

METHODS

Sprague-Dawley rats were divided into four groups. Control rats were fed a normal diet (n = 18); HC rats (n = 18) were fed 2% cholesterol diet; and HC + folate (HC+F) rats were fed an HC diet with oral folate (0.003% in water). The left femoral artery and vein were surgically excised, and angiogenesis in the ischemic limb was evaluated. We also examined the effects of Nomega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthase, on angiogenesis in the HC+F state.

RESULTS

Laser Doppler blood flow (LDBF) analysis showed lower ischemic/normal LDBF ratio in the HC group than in the control group. Angiographic and histologic analyses on day 14 revealed a smaller angiographic score (p < 0.001) and capillary density (p < 0.001) in the HC group than in controls, which were associated with reduced tissue NOx and cyclic guanosine monophosphate (cGMP) levels. The LDBF ratio, angiographic score, and capillary density were significantly restored in the HC+F group (p < 0.01 vs. HC), which were associated with increased serum folate and tissue NOx and cGMP levels. Finally, L-NAME treatment abolished the beneficial action of folate on angiogenesis in the HC state.

CONCLUSIONS

Ischemia-induced angiogenesis was inhibited by HC, which was rescued by oral folate supplementation, at least in part, via an NO-dependent manner.

Hyperhomocysteinemia impairs angiogenesis in response to hindlimb ischemia

Hyperhomocysteinemia (HH) is an independent risk factor for atherosclerosis, including peripheral arterial occlusive disease (PAOD). Because angiogenesis and collateral vessel formation are important self-salvage mechanisms for ischemic PAOD, we examined whether HH modulates angiogenesis in vivo in a rat model of hindlimb ischemia. Rats were divided into 3 groups: the control group was given tap water, the HH group was given water containing L-methionine (1 g x kg(-1) x d(-1)), and the HH+L-arg group was given water containing methionine (1 g x kg(-1) x d(-1)) and l-arginine (2.25 vol%). At day 14 of the dietary modifications, the left femoral artery and vein were excised, and the extent of angiogenesis and collateral vessels in the ischemic limb were examined for 4 weeks. Plasma homocysteine levels significantly increased (P:<0.001), and plasma and tissue contents of nitrite+nitrate as well as tissue cGMP levels significantly decreased in the HH group compared with the control group (P:<0.01). Laser Doppler blood flowmetry (LDBF) revealed a significant decrease in the ischemic/normal limb LDBF ratio in the HH group at days 7, 14, 21, and 28 (P:<0.01 versus control). Angiography revealed a significant decrease in the angiographic score in the HH group at day 14 (P:<0.001 versus control). Immunohistochemistry of ischemic tissue sections showed a significant reduction in the capillary density in the HH group (P:<0. 001 versus control). Oral l-arginine supplementation in rats with HH (HH+L-arg) restored the decreased plasma and tissue nitrite+nitrate and cGMP contents (P:<0.05) as well as angiogenesis, as assessed by LDBF (P:<0.05 versus HH), angiographic score (P:<0.01 versus HH), and capillary density (P:<0.001 versus HH). In summary, HH impaired ischemia-induced angiogenesis and collateral vessel formation in a rat model of hindlimb ischemia in vivo. The mechanism of the HH-induced impairment of angiogenesis might be mediated in part by a reduced bioactivity of endogenous NO in the HH state.

Determination of thiamine by high-performance liquid chromatography

High-performance liquid chromatographic methods for the determination of thiamine (vitamin B1) in foodstuffs or biological tissues and fluids are outlined and discussed. The methods are often similar and interchangeable, sample extraction and clean up procedures being the major difference. Most of the methods use either ultraviolet or fluorescence detection. Fluorescence detection requires either precolumn or postcolumn oxidation of thiamine to thiochrome. A number of methods are recommended and problems with standardization are emphasized.

Reduced thiamine phosphate, but not thiamine diphosphate, in erythrocytes in elderly patients with congestive heart failure treated with furosemide

OBJECTIVES

To measure the concentrations of thiamine and thiamine esters by high-pressure liquid chromatography (HPLC) in elderly patients treated with furosemide for heart failure and in a control group.

DESIGN

A cross-sectional study of blood thiamine and thiamine ester concentrations.

SUBJECTS

Forty-one patients admitted to hospital for heart failure and 34 elderly living at home. No vitamin supplementation was allowed.

RESULTS

Compared with the healthy controls, furosemide-treated patients had significantly reduced whole blood thiamine phosphate (TP; 4.4 +/- 2.2 vs. 7.6 +/- 2.0 nmol L-1) and thiamine diphosphate (TPP; 76 +/- 21.5 vs. 91 +/- 19.8 nmol L-1) (mean +/- SD). When the thiamine concentrations were related to the haemoglobin concentrations, which were reduced in the heart failure patients, the levels of TP (nmol g-1 Hb) were 0.38 +/- 0.26 vs. 0.54 +/- 0.17 (P < 0.0001), and of TPP were 6.35 +/- 1.76 vs. 6.37 +/- 1.29 (P = 0.95). There were no differences in T and TP concentrations in plasma between the two groups.

CONCLUSIONS

The elderly patients with heart failure treated with furosemide have not reduced the storage form of thiamine, TPP, but only TP. This change is most likely not an expression of a thiamine deficiency, but rather of an altered metabolism of thiamine, which is not understood at present.

Levodopa in Parkinson's disease: neurotoxicity issue laid to rest?

Orally administered levodopa remains the most effective symptomatic treatment for Parkinson's disease. The introduction of levodopa therapy is often delayed, however, because of the fear that it might be toxic for the remaining dopaminergic neurons, and thus accelerate the deterioration of the patient's condition. Evidence for levodopa toxicity comes mainly from in vitro studies which have demonstrated that levodopa can damage dopaminergic neurons by a mechanism that probably involves oxidative stress. It is widely accepted, however, that levodopa is not toxic for healthy animals and humans who do not have Parkinson's disease. It has been argued that the lesioned mesostriatal dopaminergic system could be more vulnerable to levodopa-induced toxicity, because the brain extracellular concentrations attained by levodopa are higher when the dopaminergic system is damaged, and remaining dopaminergic neurons experience a process of compensatory hyperactivity. Evidence for in vivo levodopa toxicity in animal models of Parkinson's disease is scarce and contradictory. A comprehensive recent study failed to find any evidence of levodopa toxicity in rats with either moderate or severe lesions of the mesostriatal dopaminergic system. Concerning the hypothesis of toxicity, some recent reports have shown that levodopa can have trophic effects on dopaminergic neurons in vitro, and our own work has shown that long term levodopa therapy promotes recovery of striatal dopaminergic markers in rats with moderate nigrostriatal lesions. Given that neither epidemiological nor clinical studies have ever provided evidence to support that long term levodopa administration can accelerate the progression of Parkinson's disease, we believe that levodopa therapy should not be delayed on the basis of an unconfirmed hypothesis.

Hydrolysis of the neuropeptide N-acetylaspartylglutamate (NAAG) by cloned human glutamate carboxypeptidase II

Glutamate carboxypeptidase II may modulate excitatory neurotransmission through the catabolism of the neuropeptide N-acetylaspartylglutamate (NAAG) and possibly other endogenous peptide substrates. To investigate the molecular properties of cloned human GCP II (hGCP II), we analyzed the NAAG-hydrolytic activity conveyed by transfection of a full-length hGCP II cDNA into PC3 cells, which do not express GCP II endogenously. Membrane fractions from these cells demonstrated activity with an apparent Km of 73 nM and Vmax of 35 pmol/(mg protein*min). Activity was inhibited by EDTA and stimulated by the addition of CoCl2. Addition of GCP II inhibitors beta-NAAG, quisqualic acid and 2-(phosphonomethyl)pentanedioic acid (PMPA) inhibited hydrolysis of 2.5 nM NAAG with IC50s of 201 nM, 155 nM and 98 pM, respectively. In competition experiments designed to infer aspects of hGCP II substrate selectivity, NAAG was the most potent alpha peptide tested, with an IC50 of 26 nM. Folate derivatives and some other gamma-glutamyl peptides showed comparable affinity to that of NAAG, also displaying IC50s in the low nM range. Taken together with previous evidence demonstrating their presence in GCP II-expressing tissues, these data suggest that both NAAG and folates are good candidate substrates for GCP II in vivo.

Isolation and expression of a rat brain cDNA encoding glutamate carboxypeptidase II

N-acetylated alpha-linked acidic dipeptidase (NAALADase) hydrolyzes acidic peptides, such as the abundant neuropeptide N-acetyl-alpha-L-aspartyl-L-glutamate (NAAG), thereby generating glutamate. Previous cDNA cloning efforts have identified a candidate rat brain NAALADase partial cDNA, and Northern analyses have identified a family of related RNA species that are found only in brain and other NAALADase-expressing cells. In this report, we describe the cloning of a set of rat brain cDNAs that describe a full-length NAALADase mRNA. Transient transfection of a full-length cDNA into the PC3 cell line confers NAAG-hydrolyzing activity that is sensitive to the NAALADase inhibitors quisqualic acid and 2-(phosphonomethyl)glutaric acid. Northern hybridization detects the expression of three similar brain RNAs approximately 3,900, 3,000, and 2,800 nucleotides in length. In situ hybridization histochemistry shows that NAALADase-related mRNAs have an uneven regional distribution in rat brain and are expressed predominantly by astrocytes as demonstrated by their colocalization with the astrocyte-specific marker glial fibrillary acidic protein.

Detection and analyses of ascorbyl radical in cerebrospinal fluid and serum of acute lymphoblastic leukemia

We have detected and analyzed a free radical in human cerebrospinal fluid (CSF) of acute lymphoblastic leukemia (ALL) for the first time using electron paramagnetic resonance (EPR) at ambient temperature. We have also introduced an alternative capillary method to measure the radical. EPR spectra of the radical show a characteristic doublet with hyperfine coupling value of 1.8 G and g = 2.005. Based on EPR measurements, computer simulation, and literature values, we have determined that the species is ascorbyl radical (AsR). The radical has been investigated in CSF samples from ALL patients having no therapy, undergoing chemotherapy, and following therapy. Determination of the ascorbyl radical concentrations in CSF and serum was attempted using known concentrations of a nitroxyl radical. In addition, comparison in CSF and serum for ALL has been made along with statistical analyses of the data obtained. We found that AsR in CSF and serum has a strong correlation in patients undergoing chemotherapy (n = 57, r = 0.57, P < 0.0001). Ascorbate in CSF and serum show good correlation in patients having therapy but not for patients after therapy.

Ascorbate in healthy subjects, amyotrophic lateral sclerosis and Alzheimer's disease

The aim of the present study was to report the levels of ascorbic acid in amyotrophic lateral sclerosis (ALS) and Alzheimer's disease (AD) and the effectiveness of ascorbic acid homeostasis in the central nervous system. Plasma and CSF ascorbic acid levels were measured by high performance liquid chromatography in 19 ALS patients, 17 AD patients and 15 controls. No statistically significant difference was found between patients and controls. However, wide fluctuations of plasma concentrations were found to result in relatively stable CSF levels, by appropriate adjustments of CSF/plasma ratio. It appears that in normal subjects and in the disease under study, this ratio reflects the activity of the choroid plexus ascorbate transporter.

Ascorbic acid in cerebrospinal fluid — a possible protection against free radicals in the brain

The function of ascorbic acid in living organisms is complex. Previous studies emphasize its protective role against harmful effect of free radicals, and its presence is necessary for the function of numerous enzymes. Ascorbic acid is a powerful reducing agent due to its dienol molecular structure, which is not present in the oxidized form, dehydroascorbic acid. The ratio of ascorbic acid and dehydroascorbic acid might be a marker of oxidative-reductive processes. We measured and compared the level of ascorbic acid and dehydroascorbic acid in the plasma of healthy persons and those of senile dementia patients, who represent pathological aging of the brain. In senile dementia patients, ascorbic acid and dehydroascorbic acid levels were also measured in the cerebrospinal fluid. Concentrations were determined by high performance liquid chromatography with electrochemical detection. In the plasma of senile dementia patients, very low ascorbic acid levels were found (ca. 30% of the healthy control). In lumbar cerebrospinal fluid, the concentration of ascorbic acid is 2.7 times higher compared to that of the plasma level. After intravenous infusion of ascorbic acid, a slow but marked increase of the concentration in the cerebrospinal fluid was measured. Our results support an active transport process for ascorbic acid through the blood-CSF barrier. Ascorbic acid level might be an important factor representing the protection of the central nervous system against free radicals.

The total peroxyl radical-trapping ability of plasma and cerebrospinal fluid in normal and preeclamptic parturients

Plasma and cerebrospinal fluid total peroxyl radical-trapping antioxidative parameter (TRAP) and the main antioxidant components of TRAP (vitamin E, ascorbic acid, uric acid, protein sulfhydryl groups, and the unidentified antioxidant proportion) were analyzed in 11 preeclamptic parturients, 9 healthy parturients with an uncomplicated pregnancy, and 10 healthy nonpregnant women. In addition, the possible effects of ongoing labor were studied in 10 healthy parturients. The samples of plasma and cerebrospinal fluid (CSF) were collected at cesarean section (pregnant women) or minor surgical procedure (nonpregnant women). Normal pregnancy or ongoing labor induced no significant changes in total TRAP, as compared with nonpregnant women, but significant changes in the percentage contributions of individual antioxidants were noted in plasma and CSF. In preeclampsia, a significant increase in TRAP was noted in both plasma and CSF. This increase was mainly due to an increased proportion of uric acid and unidentified antioxidants in plasma samples, and an increased proportion of unidentified antioxidants in CSF. The concentration of CSF ascorbic acid was decreased in preeclampsia, and a negative correlation between CSF ascorbic acid and blood pressure was observed.

Alcoholic cognitive deterioration and nutritional deficiencies

Chronic alcoholic patients frequently exhibit a mild to moderate cognitive impairment that has been related to Wernicke-Korsakoff encephalopathy and attributed tentatively to nutritional and vitamin deficiencies. To elucidate the possible relation between alcoholic cognitive deterioration (ACD) and nutritional and vitamin deficiencies, several tests of intelligence and memory were administered to 54 chronic alcoholic patients and 30 controls. Serum levels of thiamine, folic acid, vitamins B12, A, and E, and certain nutritional indexes were determined in most of the subjects. The alcoholics scored significantly lower in intellectual and visuospatial tasks but not in verbal memory tasks. They had a lower serum level for thiamine but not of the remaining vitamins. However, the correlations between serum thiamin and cognitive performance scores were low, and according to stepwise regression analysis, duration of alcohol intake and education were the variables with predictive value for intellectual and memory test performance. These results suggest that serum thiamin deficiency is not the main pathogenetic factor related to ACD.

Ascorbate concentration in human cerebrospinal fluid (CSF) and serum. Intrathecal accumulation and CSF flow rate

Concentrations of ascorbate (vitamin C) in cerebrospinal fluid (CSF) from human controls (median 163 mumol/l, n = 63) were found to be in the same range as CSF samples from patients (n = 56) with various neurological diseases, but excluding those with blood-CSF barrier dysfunction. The CSF/serum concentration ratio in the former group is non-linear, decreasing with increasing serum concentration. Surprisingly, ascorbate concentration in blood (median 41 mumol/l, n = 119) was decreased significantly in cases of neurological diseases with a blood-CSF barrier dysfunction (median 26 mumol/l, n = 30). In this latter group a linear CSF to serum ratio with a mean of 5.7:1 (with CSF/serum albumin quotients QAlb = 7.8-70.8 x 10(-3), median 10.0 x 10(-3)) was observed, approaching a value > 12.5:1 in the case of complete stop of CSF flow. Serum ascorbate concentrations decreased with decreasing CSF flow rate (1 square root of QAlb), indicating a CSF flow-dependent constant contribution from high intrathecal ascorbate concentration to the varying diet-dependent concentrations in blood. In the control group the biological coefficient of variation for CSF ascorbate concentrations (C.V. = 21.1%) was smaller than for serum concentrations (C.V. = 42.6%), confirming an efficient ascorbate homeostasis in human brain. This was different from uric acid which was used as a reference molecule with an inversed gradient in the same group of control patients. Similar variations in CSF(y) and serum(x) for urate concentrations are observed due to the strong correlation y = 0.1x +/- 10 mumol/l, including 99% of the cases with an urate serum concentration range from 80 mumol/l to 460 mumol/l.

Thiamin and thiamin phosphate ester deficiency assessed by high performance liquid chromatography in four clinical cases of Wernicke encephalopathy

The concentrations of thiamin and thiamin phosphate esters were determined by high performance liquid chromatography in four patients with clinical Wernicke encephalopathy. Three were alcohol abusers, and one had prolonged vomiting and anorexia. Thiamin and thiamin monophosphate were assessed in plasma and whole blood (four patients) and in cerebrospinal fluid (two patients) before and during thiamin treatment. Thiamin diphosphate was also assessed in whole blood in the four patients. Before treatment, thiamin monophosphate was significantly decreased in all patients, and thiamin diphosphate in three. A poor increase in thiamin mono- and diphosphate was paralleled by a slow clinical improvement in one patient, while an increase in all thiamin compounds was observed in two patients with a rapid recovery. Thiamin monophosphate was a more sensitive marker of deficiency than thiamin diphosphate and unphosphorylated thiamin.