Folic acid deficiency and homocysteine impair DNA repair in hippocampal neurons and sensitize them to amyloid toxicity in experimental models of Alzheimer's disease

Increase of total homocysteine concentration in cerebrospinal fluid in patients with Alzheimer's disease and Parkinson's disease

We determined the concentrations of free homocysteine (HC) and total HC in the cerebrospinal fluid (CSF) of patients with Alzheimer's disease (AD) or Parkinson's disease (PD) in order to elucidate whether HC is related to the pathogenesis of these neurodegenerative diseases. The concentration of free HC did not differ significantly from that of the normal controls, while the concentration of total HC was significantly higher in the AD and PD patients (+31% in AD,+31% in PD; p<0.05). These findings suggest that an increase of total HC concentration in the brain is commonly seen in patients with AD and PD, and this may be related to the pathogenesis of these two diseases.

Neurological impairment in fetal mouse brain by drinking water disinfectant byproducts

Developmental exposure to environmental chemicals may have detrimental effects on embryonic brains that could play a major role in the etio-pathology of fetal and adult neurological diseases. The exact mechanism by which prenatal exposures to environmental agents, such as drinking water disinfectant byproducts (DBP), cause neurological impairment in fetus is not known. Our objective is to examine the impact of prenatal exposure to DBP on fetal brain development. Pregnant CD-1 mice, at the sixth day of gestation (GD-6), received a daily (GD-6-GD-18) oral dose of chloroacetonitrile (CAN, 25 ppm), a member of DBP. To assess fetal brain uptake of CAN, several animals were injected with a tracer dose of 2-[(14)C]-CAN (333 microCi/kg, i.v.), at GD-12 and processed for quantitative in situ micro whole-body autoradiography (QIMWBA) at 1 and 24 h after treatment. The remaining animals continued receiving CAN until GD-18 when fetal brains were processed for biochemical determination of oxidative stress (OS) or prepared for histological examinations. The results indicate a rapid placental transfer and fetal brain uptake of 2-[(14)C]-CAN/metabolites in cortical areas and hippocampus. In treated animals 3-fold decrease in glutathione (GSH), 1.3-fold increase in lipid peroxidation and 1.4-fold increase in DNA oxidation were detected as compared to control. DeOlmos cupric silver staining of fetal brains indicated significant increase in cortical neurodegeneration in treated animals. Immunohistochemical labeling (TUNEL) of apoptotic nuclei in the cortices and choroid plexuses were also increased in treated animals as compared to control. In conclusion, CAN crosses the placental and fetal blood-brain barriers and induces OS that triggered apoptotic neurodegenration in fetal brain. Future studies will examine the molecular mechanisms of these events and its impact on neural development of offspring.

Activation of catechol-O-methyltransferase in astrocytes stimulates homocysteine synthesis and export to neurons

Elevation of the total homocysteine (tHcy) concentration in plasma has been implicated in neurodegeneration in patients with stroke, dementia, Alzheimer disease, and Parkinson disease. Because the mechanisms controlling brain tHcy are unknown, the present study investigated its synthesis and transport in primary rat brain cell cultures. We found that the catechol-O-methyltransferase (COMT) substrate 3,4-dihydroxybenzoic acid (DHB) increased export of tHcy in astrocytes, but not in neurons. The export mechanism was selective for tHcy over cyst(e)ine, total glutathione (tGSH) or cysteinylglycine (Cys-Gly). tHcy export from astrocytes was also induced by the COMT substrates levodopa (L-DOPA), dopamine and quercetin, and it was blocked by the COMT inhibitors tropolone and entacapone. This export was associated with increased synthesis of tHcy because both intracellular and extracellular tHcy concentrations rose during COMT activation. Incubation in cyst(e)ine-deficient medium inhibited the tHcy export response to COMT activation. Exogenous tHcy (100 muM) was accumulated into neurons, but not into astrocytes. We conclude that activation of COMT causes sustained synthesis of Hcy in astrocytes and transport of this amino acid to neurons.

A Cross-sectional Study of Homocysteine-, NO-levels, and CT-findings in Alzheimer Dementia, Vascular Dementia and Controls

Repetitive measurement with neuroimaging techniques could be useful instruments permitting to differentiate between Alzheimer disease (AD) and vascular dementia (VD). The major genetic risk factor for the development of late-onset AD is the allele epsilon4 of the apolipoprotein E (ApoE). Moreover nitric oxide (NO) and homocysteine (Hcy) seems to be correlated with the degree of cognitive impairment in demented subjects. The aim of this study was to investigate the association between serum NO and Hcy levels, global brain atrophy and brain vascular lesion in AD and VD patients. We report that high plasma levels of homocysteine resulted associated with AD and VD, suggesting that in AD elevated plasma Hcy might be a consequence of concomitant vascular dementia. Otherwise, plasma NO levels were not significantly different in any of the groups. Moreover, neuroimaging measures of vascular lesion level could be of usefulness to differentiate between AD and VD.

Reduced risk of Alzheimer's disease with high folate intake: the Baltimore Longitudinal Study of Aging

BACKGROUND

Study findings have suggested an association between Alzheimer's disease (AD) risk and several vitamins and have speculated about their use as preventive agents. Here, we examine whether total intake (intake from diet plus supplements) of antioxidant vitamins (E, C, carotenoids) and B vitamins (folate, B(6), and B(12)) is associated with a reduced risk of AD.

METHODS

Participants were 579 nondemented elderly volunteers from the Baltimore Longitudinal Study of Aging who completed dietary diaries and recorded supplement intake for a 7-day period. Cox regression was used to estimate the relative risk (RR) of AD associated with total vitamin intake categorized into levels above or below the Recommended Dietary Allowance (RDA).

RESULTS

After a mean follow-up of 9.3 years, AD developed in 57 participants. Higher intake of folate (RR, 0.41; 95% confidence interval [CI], 0.22 to 0.76), vitamin E (RR, 0.56; 95% CI, 0.30 to 1.06), and vitamin B(6) (RR, 0.41; 95% CI, 0.20 to 0.84) were associated individually with a decreased risk of AD after adjusting for age, gender, education, and caloric intake. When these 3 vitamins were analyzed together, only total intake of folate at or above the RDA (RR, 0.45; 95% CI, 0.21 to 0.97) was associated with a significant decreased risk of AD. No association was found between total intake of vitamins C, carotenoids, or vitamin B(12) and risk of AD.

CONCLUSIONS

These findings suggest that total intake of folate at or above the RDA is associated with a reduced risk of AD. Additional studies are necessary to further investigate whether folate or other(s) unmeasured factor(s) may be responsible for this reduction in risk.

Folate deficiency inhibits proliferation of adult hippocampal progenitors

Neurogenesis in the adult hippocampus may play important roles in learning and memory, and in recovery from injury. As recent findings suggest, the perturbance of homocysteine/folate or one-carbon metabolism can adversely affect both the developing and the adult brain, and increase the risk of neural tube defects and Alzheimer's disease. We report that dietary folic acid deficiency dramatically increased blood homocysteine levels and significantly reduced the number of proliferating cells in the dentate gyrus of the hippocampus in adult mice. In vitro, the perturbance of one-carbon metabolism repressed proliferation of cultured embryonic multipotent neuroepithelial progenitor cells and affected cell cycle distribution. Our results suggest that dietary folate deficiency inhibits proliferation of neuronal progenitor cells in the adult brain and thereby affects neurogenesis.

Fruit and vegetable consumption and cognitive decline in aging women

We prospectively examined fruit and vegetable intake in relation to cognitive function and decline among aging women. Participants were followed from in 1976 with biennial questionnaires, and food frequency questionnaires were administered in 1984, 1986, and every 4 years thereafter. From 1995 to 2001, we administered, by telephone, six cognitive tests measuring general cognition, verbal memory, category fluency, and working memory. We repeated assessments two years later for 13,388 women (>90% follow-up). We averaged dietary intakes from 1984 through the first cognitive assessment, and used linear regression to obtain multivariable-adjusted mean differences in performance and decline in performance across intake levels. Fruits were not associated with cognition or cognitive decline. However, total vegetable intake was significantly associated with less decline. Specifically, on a global score combining all tests, women in the highest quintile of cruciferous vegetables declined slower (by 0.04 unit; 95% confidence interval, 0.003, 0.07; p trend = 0.1) compared with the lowest quintile. Women consuming the most green leafy vegetables also experienced slower decline than women consuming the least amount (by 0.05 unit; 95% confidence interval, 0.02, 0.09; p trend < 0.001). These mean differences were equivalent to those observed for women about 1 to 2 years apart in age.

Peroxynitrite-mediated oxidation of the C85S/C152E mutant of dihydrofolate reductase from Escherichia coli: functional and structural effects

Peroxynitrite is a potent reactive oxygen species that is believed to mediate deleterious protein modifications in a wide variety of neurodegenerative disorders. In this study, we have analysed the effects of oxidative damage induced by peroxynitrite on a cysteine-free mutant of dihydrofolate reductase (SE-DHFR), from a functional and a structural point of view. The peroxynitrite-mediated oxidation results in the inhibition, concentration-dependent, of the catalytic activity. This effect is strongly influenced by the HCO(3)(-)/CO(2) buffering system, that we observed to significantly affect the yield of protein oxidation by modulating the peroxynitrite-induced modification of aromatic residues. Because of this effect, in presence of bicarbonate system, we have observed a protection of enzymatic activity of SE-DHFR with regard to peroxynitrite. The thermodynamic stability of the oxidized protein has been studied in comparison with the non-oxidized protein by differential scanning calorimetry. The thermodynamic parameters obtained showed a decrease of stability of SE-DHFR upon oxidation, evaluated in terms of Gibbs free energy of about 1.25 kcal/mol at 25 degrees C, with respect to the non-oxidized protein. Together, these data indicate that structural and functional alterations induced by peroxynitrite may play a direct role in compromising DHFR function in multiple pathological conditions.

Homocysteine versus the vitamins folate, B6, and B12 as predictors of cognitive function and decline in older high-functioning adults: MacArthur Studies of Successful Aging

BACKGROUND

Elevated plasma total homocysteine concentration may be a risk factor for cognitive decline and Alzheimer disease, but data from prospective studies are limited. Further, high homocysteine levels are associated with low vitamin status, and it is unknown whether it is homocysteine toxicity or vitamin insufficiency that is responsible for the observed cognitive dysfunction.

METHODS

We performed cross-sectional and longitudinal analyses of a cohort of 499 high-functioning community-dwelling persons aged 70 to 79 years to determine the effect of homocysteine and related vitamin plasma concentrations on cognitive function and cognitive decline. Nonfasting plasma concentrations of homocysteine, folate, vitamin B(6), and vitamin B(12) were measured at baseline. Summary measures of cognitive function were created from tests of multiple cognitive domains administered at baseline and again after 7 years.

RESULTS

In cross-sectional analyses investigating each variable separately, subjects with elevated homocysteine levels, or low levels of folate or vitamin B(6), demonstrated worse baseline cognitive function. In longitudinal analyses, after adjusting for multiple covariates, including homocysteine, those in the bottom quartile of folate had a 1.6-fold increased risk (95% confidence interval: 1.01 to 2.31; P =0.04) of being in the worst quartile of 7-year cognitive decline. Low folate levels largely accounted for a trend towards greater cognitive decline with elevated homocysteine level.

CONCLUSION

In high-functioning older adults, low folate levels appear to be a risk factor for cognitive decline. The risk of developing cognitive decline might be reduced through dietary folate intake.

Early dysregulation of hippocampal proteins in transgenic rats with Alzheimer's disease-linked mutations in amyloid precursor protein and presenilin 1

The response of the hippocampal proteome to expression of mutant proteins present in familial forms of Alzheimer's disease (AD) was studied using transgenic rats. These animals carry both the amyloid precursor protein Swedish and 717 mutation (APP(SW+717)) as well as the presenilin 1 Finnish mutation (PS1(FINN)). This transgenic rat model displays intracellular amyloid beta (Abeta) in neurons of the neocortex and the hippocampus (CA2 and CA3). The hippocampus was selected as it is one of the first brain regions affected in AD and is involved in the processing of short-term memory and spatial memory. Applying a proteomic approach, we demonstrate that the expression of APP(SW+717) and PS1(FINN) transgenes causes changes in expression of hippocampal proteins, some of which have been previously linked to learning and memory formation. The protein alterations documented here occur in the absence of plaque formation and prior to the onset of cognitive deficits later observed in these transgenic rats. This indicates that molecular changes take place in the hippocampal neurons in response to expression of mutant proteins APP(SW+717) and PS1(FINN), which precede the occurrence of overt extracellular accumulation of extracellular amyloid. The implications of these findings on our understanding of the early stages of AD are discussed.

Melatonin inhibits neural apoptosis induced by homocysteine in hippocampus of rats via inhibition of cytochrome c translocation and caspase-3 activation and by regulating pro- and anti-apoptotic protein levels

In the present study, we examined the molecular mechanism by which homocysteine causes neuronal cell apoptosis. We further investigated the mechanisms of melatonin's ability to reduce homocysteine-induced apoptosis. Consistent with its antioxidant properties, melatonin reduced homocysteine-induced lipid peroxidation and stimulated glutathione peroxidase enzyme activity in hippocampus of rats with hyperhomocysteinemia. Furthermore, melatonin treatment diminished cytochrome c release from mitochondria and reduced caspase 3 and caspase 9 activation induced by hyperhomocysteinemia. Chronic hyperhomocysteinemia also led to poly(ADP-ribose) polymerase cleavage and subsequently DNA fragmentation. Treatment with melatonin markedly inhibited poly(ADP-ribose) polymerase cleavage and reduced DNA damage. Hyperhomocysteinemia caused an elevation of pro-apoptotic Bax levels while reducing anti-apoptotic protein, Bcl-2, levels. Daily administration of melatonin up-regulated Bcl-2 and down-regulated Bax levels. We propose that, in addition to its antioxidant properties, melatonin has the ability to protect neuronal cells against apoptosis mediated homocysteine neurotoxicity by modulating apoptosis-regulatory proteins in the hippocampus of rats.

S-adenosylmethionine/homocysteine cycle alterations modify DNA methylation status with consequent deregulation of PS1 and BACE and beta-amyloid production

Few diseases are characterized by high homocysteine (HCY) and low folate and vitamin B12 blood levels. Alzheimer disease (AD) is among these. It has already been shown that DNA methylation is involved in amyloid precursor protein (APP) processing and beta-amyloid (A beta) production through the regulation of Presenilin1 (PS1) expression and that exogenous S-adenosylmethionine (SAM) can silence the gene reducing A beta production. Here we demonstrate that BACE (beta-secretase), as well as PS1, is regulated by methylation and that the reduction of folate and vitamin B12 in culture medium can cause a reduction of SAM levels with consequent increase in presenilin1 and BACE levels and with increase in A beta production. The simultaneous administration of SAM to the deficient medium can restore the normal gene expression, thus reducing the A beta levels. The use of deprived medium was intended to mimic a mild nutritional deficit involved in the onset of AD.

Folate deficiency increases postischemic brain injury

BACKGROUND AND PURPOSE

Folate deficiency and resultant hyperhomocysteinemia impair vascular function and increase stroke risk. We tested the hypothesis that folate deficiency and high homocysteine levels promote DNA damage and increase brain injury after cerebral ischemia/reperfusion.

METHODS

129/Sv mice, uracil-DNA glycosylase-deficient (Ung-/-) mice, and Ung+/+ littermate mice were exposed to a folate-deficient diet for 3 months and then subjected to 30-minute middle cerebral artery (MCA) occlusion and reperfusion. Plasma homocysteine levels and physiological parameters were measured in selected animals. Outcome measures were neurological sensorimotor deficits, infarct size measured by computer-assisted volumetry, and oxidative DNA damage measured by a colorimetric assay.

RESULTS

Exposure to a folate-deficient diet for 3 months conferred approximately 6- to 10-fold higher plasma homocysteine levels than those associated with a normal diet. Cerebral lesion volumes and neurological deficits after MCA occlusion and 72-hour reperfusion were significantly 2.1-fold increased in folate-deficient 129/SV wild-type mice compared with those associated with a normal diet, which could not be explained by obvious differences in physiological parameters. Abasic sites, hallmarks of oxidative DNA damage, were significantly increased in DNA from the ischemic brain of folate-deficient animals at early time points after MCA occlusion. Folate deficiency further increased brain lesion size in animals lacking uracil-DNA glycosylase compared with wild-type littermate mice.

CONCLUSIONS

Folate deficiency and resultant hyperhomocysteinemia are not only associated with increased stroke risk but increase oxidative DNA damage and ischemic lesion size after MCA occlusion/reperfusion.

Dopaminergic neurotoxicity of homocysteine and its derivatives in primary mesencephalic cultures

Levodopa and dopamine are metabolized to 3-O-methyldopa and 3-methoxytyramine, respectively, by the enzyme catechol-O-methyltransferase (COMT) leading to the production of the demethylated cofactor S-adenosylhomo-cysteine (SAH) and subsequently homocysteine (HC). Indeed, treatment of Parkinson's disease (PD) patients with levodopa leads to increased HC blood levels. Therefore, HC is discussed to be involved in the pathogenesis of PD as well as in enhanced progression of PD in patients treated with levodopa. Here we investigated the toxicity of HC and its derivatives SAH, homocysteic acid (HCA) and cysteic acid (CA) on tyrosine hydroxylase (TH)-positive neurons in primary mesencephalic cultures from rat in vitro. Furthermore, we evaluated the toxicity of HC on cultures stressed with the dopaminergic neurotoxin 1-methyl-4-phenylpyridinium (MPP+). Incubation with HC or HCA did not result in significant effects on TH-positive neuron survival with concentrations up to 1 mM, but led to morphological changes of TH-positive cells with significantly fewer and shorter neurites at concentrations of > or = 100 microM after 48 h. In contrast, SAH and CA were toxic at concentrations of >100 microM after 48h. Furthermore, MPP+ showed strong toxicity towards TH-positive cells after 48 h (half-maximal toxic concentration: 20 microM), whereas co-incubation with HC for 24 or 48 h did not further alter TH-positive cell survival. Taken together, our results do not demonstrate relevant dopaminergic toxicity of HC in vitro, and therefore HC is most likely not involved in the pathogenesis of PD or in accelerating the progression of PD by levodopa.

Dietary factors and Alzheimer's disease

Alzheimer's disease (AD) is increasing in prevalence, and environmental risk factors have not been identified with certainty. There is evidence that oxidative stress, homocysteine-related vitamins, fats, and alcohol have a role in the pathogenesis of AD. Few large epidemiological studies have explored the associations between nutrients and AD, and there has been only one trial of vitamin E in the prevention of AD. Some studies suggest that high intake of vitamins C, E, B6, and B12, and folate, unsaturated fatty acids, and fish are related to a low risk of AD, but reports are inconsistent. Modest to moderate alcohol intake, particularly wine, may be related to a low risk of AD. Available data do not permit definitive conclusions regarding diet and AD or specific recommendations on diet modification for the prevention of AD.

Suppression of uracil-DNA glycosylase induces neuronal apoptosis

A chronic imbalance in DNA precursors, caused by one-carbon metabolism impairment, can result in a deficiency of DNA repair and increased DNA damage. Although indirect evidence suggests that DNA damage plays a role in neuronal apoptosis and in the pathogenesis of neurodegenerative disorders, the underlying mechanisms are poorly understood. In particular, very little is known about the role of base excision repair of misincorporated uracil in neuronal survival. To test the hypothesis that repair of DNA damage associated with uracil misincorporation is critical for neuronal survival, we employed an antisense (AS) oligonucleotide directed against uracil-DNA glycosylase encoded by the UNG gene to deplete UNG in cultured rat hippocampal neurons. AS, but not a scrambled control oligonucleotide, induced apoptosis, which was associated with DNA damage analyzed by comet assay and up-regulation of p53. UNG mRNA and protein levels were decreased within 30 min and were undetectable within 6-9 h of exposure to the UNG AS oligonucleotide. Whereas UNG expression is significantly higher in proliferating as compared with nonproliferating cells, such as neurons, the levels of UNG mRNA were increased in brains of cystathionine beta-synthase knockout mice, a model for hyperhomocysteinemia, suggesting that one-carbon metabolism impairment and uracil misincorporation can induce the up-regulation of UNG expression.

Plasma amino acid concentrations in patients with amnestic mild cognitive impairment or Alzheimer disease

BACKGROUND

Plasma concentrations of several amino acids may affect the availability of important neurotransmitter precursors in the brain. Abnormalities in the plasma amino acid profile have been reported in elderly persons with cognitive impairment, but no data exist for the prodromal phase of Alzheimer disease (AD), which is characterized by amnestic mild cognitive impairment (aMCI).

OBJECTIVE

The objective was to investigate whether the plasma amino acid profiles of elderly patients with aMCI or AD are abnormal.

DESIGN

The plasma amino acid profile was assessed in 29 cognitively normal control subjects (age: 86.7 +/- 5.9 y), 21 patients with aMCI (age: 84.9 +/- 7.0 y), and 51 patients with AD (age: 86.7 +/- 5.4 y). The participants were from the University of Bologna Research Center for Physiopathology of Aging, Italy.

RESULTS

Higher plasma concentrations of the aromatic amino acid phenylalanine were found in the aMCI (68 micromol/L; 95% CI: 63, 73) and AD (62 micromol/L; 95% CI: 59, 65) patients than in the control subjects (54 micromol/L; 95% CI: 48, 61; P < 0.05). The ratio of arginine to other basic amino acids was also higher in the aMCI (0.31 +/- 0.04) and AD (0.27 +/- 0.08) patients than in the control subjects (0.21 +/- 0.05; P < 0.05). Adjustment for differences in body composition, serum vitamin B-12 concentrations, and serum folate concentrations did not significantly affect the results.

CONCLUSIONS

The plasma amino acid profiles of elderly patients with aMCI or AD show abnormalities in aromatic and basic amino acids that potentially affect neurotransmitter biosynthesis.

Imbalanced Base Excision Repair in Response to Folate Deficiency Is Accelerated by Polymerase β Haploinsufficiency

The mechanism by which folate deficiency influences carcinogenesis is not well established, but a phenotype of DNA strand breaks, mutations, and chromosomal instability suggests an inability to repair DNA damage. To elucidate the mechanism by which folate deficiency influences carcinogenicity, we have analyzed the effect of folate deficiency on base excision repair (BER), the pathway responsible for repairing uracil in DNA. We observe an up-regulation in initiation of BER in liver of the folate-deficient mice, as evidenced by an increase in uracil DNA glycosylase protein (30%, p < 0.01) and activity (31%, p < 0.05). However, no up-regulation in either BER or its rate-determining enzyme, DNA polymerase beta (beta-pol) is observed in response to folate deficiency. Accordingly, an accumulation of repair intermediates in the form of DNA single strand breaks (37% increase, p < 0.03) is observed. These data indicate that folate deficiency alters the balance and coordination of BER by stimulating initiation without subsequently stimulating the completion of repair, resulting in a functional BER deficiency. In directly establishing that the inability to induce beta-pol and mount a BER response when folate is deficient is causative in the accumulation of toxic repair intermediates, beta-pol-haploinsufficient mice subjected to folate deficiency displayed additional increases in DNA single strand breaks (52% increase, p < 0.05) as well as accumulation in aldehydic DNA lesions (38% increase, p < 0.01). Since young beta-polhaploinsufficient mice do not spontaneously exhibit increased levels of these repair intermediates, these data demonstrate that folate deficiency and beta-pol haploinsufficiency interact to increase the accumulation of DNA damage. In addition to establishing a direct role for beta-pol in the phenotype expressed by folate deficiency, these data are also consistent with the concept that repair of uracil and abasic sites is more efficient than repair of oxidized bases.

Folic acid supplementation enhances repair of the adult central nervous system

Folic acid supplementation has proved to be extremely effective in reducing the occurrence of neural tube defects (NTDs) and other congenital abnormalities in humans, suggesting that folic acid can modulate key mechanisms for growth and differentiation in the central nervous system (CNS). To prevent NTDs, however, supplemental folate must be provided early in gestation. This suggests that the ability of folic acid to activate growth and differentiation mechanisms may be confined to the early embryonic period. Here, we show that folic acid can enhance growth and repair mechanisms even in the adult CNS. Using lesion models of CNS injury, we found that intraperitoneal treatment of adult rats with folic acid significantly improves the regrowth of sensory spinal axons into a grafted segment of peripheral nerve in vivo. Regrowth of retinal ganglion cell (RGC) axons into a similar graft also was enhanced, although to a smaller extent than spinal axons. Furthermore, folic acid supplementation enhances neurological recovery from a spinal cord contusion injury, showing its potential clinical impact. The results show that the effects of folic acid supplementation on CNS growth processes are not restricted to the embryonic period, but can also be effective for enhancing growth, repair, and recovery in the injured adult CNS.

Folic acid in the monkey brain: an immunocytochemical study

The present report describes the first visualization of folic acid-immunoreactive fibers in the mammalian central nervous system using a highly specific antiserum directed against this vitamin. The distribution of folic acid-immunoreactive structures was studied in the brainstem and thalamus of the monkey using an indirect immunoperoxidase technique. We observed fibers containing folic acid, but no folic acid-immunoreactive cell bodies were found. In the brainstem, no immunoreactive structures were visualized in the medulla oblongata, pons, or in the medial-caudal mesencephalon, since at this location immunoreactive fibers containing folic acid were only found at the rostral level in the dorsolateral mesencephalon (in the mesencephalic-diencephalic junction). In the thalamus, the distribution of folic acid-immunoreactive structures was more widespread. Thus, we found immunoreactive fibers in the midline, in nuclei close to the midline (dorsomedial nucleus, centrum medianum/parafascicular complex), in the ventral region of the thalamus (ventral posteroinferior nucleus, ventral posteromedial nucleus), in the ventrolateral thalamus (medial geniculate nucleus, lateral geniculate nucleus, inferior pulvinar nucleus) and in the dorsolateral thalamus (lateral posterior nucleus, pulvinar nucleus). The highest density of fibers containing folic acid was observed in the dorsolateral mesencephalon and in the pulvinar nucleus. The distribution of folic acid-immunoreactive structures in the monkey brain suggests that this vitamin could be involved in several mechanisms, such as visual, auditory, motor and somatosensorial functions.

Homocysteine and methylenetetrahydrofolate reductase polymorphism in Alzheimer's disease

Homocysteine metabolism is influenced by genetic polymorphisms of the methylenetetrahydrofolate reductase (MTHFR 677 C-->T and 1298 A-->C) and transcobalamin genes (TCN1 776 C-->G ). We evaluated the association of homocysteine with Alzheimer's disease (AD) and the influence of related polymorphisms and APOE, in 180 cases and 181 controls from southern Italy. Homocysteine (upper tercile) was associated with AD risk, with an odds ratio of 2.8 (95% confidence interval (CI) 1.54-5.22, p=0.0008), which was increased 2.2- and 2.0-fold by MTHFR 677T (odds ratio 6.28, 95% CI 2.88-16.20, p < 0.0001) and APOE epsilon4 (odds ratio: 5.60, 95% CI 1.12-28.05, p=0.0361), respectively. In conclusion, association of homocysteine with AD was aggravated by MTHFR 677T and APOE epsilon4 alleles.

Metal-catalyzed disruption of membrane protein and lipid signaling in the pathogenesis of neurodegenerative disorders

Membrane lipid peroxidation and oxidative modification of various membrane and associated proteins (e.g., receptors, ion transporters and channels, and signal transduction and cytoskeletal proteins) occur in a range of neurodegenerative disorders. This membrane-associated oxidative stress (MAOS) is promoted by redox-active metals, most notably iron and copper. The mechanisms whereby different genetic and environmental factors initiate MAOS in specific neurological disorders are being elucidated. In Alzheimer's disease (AD), the amyloid beta-peptide generates reactive oxygen species and induces MAOS, resulting in disruption of cellular calcium homeostasis. In Parkinson's disease (PD), mitochondrial toxins and perturbed ubiquitin-dependent proteolysis may impair ATP production and increase oxyradical production and MAOS. The inheritance of polyglutamine-expanded huntingtin may promote neuronal degeneration in Huntington's disease (HD), in part, by increasing MAOS. Increased MAOS occurs in amyotrophic lateral sclerosis (ALS) as the result of genetic abnormalities (e.g., Cu/Zn-superoxide dismutase mutations) or exposure to environmental toxins. Levels of iron are increased in vulnerable neuronal populations in AD and PD, and dietary and pharmacological manipulations of iron and copper modify the course of the disease in mouse models of AD and PD in ways that suggest a role for these metals in disease pathogenesis. An increasing number of pharmacological and dietary interventions are being identified that can suppress MAOS and neuronal damage and improve functional outcome in animal models of AD, PD, HD, and ALS. Novel preventative and therapeutic approaches for neurodegenerative disorders are emerging from basic research on the molecular and cellular actions of metals and MAOS in neural cells.

Homocysteine as a neurotoxin in chronic alcoholism

There is evidence from in vitro and in vivo studies that homocysteine induces neuronal damage and cell loss by both excitotoxicity and different apoptotic processes. Clinical evidence suggest a strong relationship between higher plasma homocysteine levels and brain atrophy in healthy elderly subjects as well as in elderly at risk of and with Alzheimer's disease. Chronic alcoholism leads to elevated plasma homocysteine levels, as shown by clinical investigations and animal experiments. In addition, an association between brain atrophy and increased levels of homocysteine in chronic alcoholism was shown. This may have important implications for the pathogenesis of alcoholism-associated brain atrophy. Furthermore, taking into account that high plasma homocysteine levels are helpful in the prediction of alcohol withdrawal seizures, early anticonvulsive therapy could prevent this severe complication. Homocysteine plays a role in a shared biochemical cascade involving overstimulation of N-methyl-D-aspartate (NMDA) receptors, oxidative stress, activation of caspases, DNA damage, endoplasmic reticulum and mitochondrial dysfunction. These mechanisms are believed to be important in the pathogenesis of both excitotoxicity and apoptotic neurotoxicity. Prospective intervention studies may show whether the incidence of complications of alcohol withdrawal or alcoholism-associated disorders can be reduced by therapeutic measures with early lowering of elevated homocysteine levels (e.g. folate administration). The most important pathophysiological and pathobiochemical features of glutamatergic neurotransmission and of ethanol-induced hyperhomocysteinaemia are reviewed in relation to their excitotoxic and apoptotic potential.

Increased transcription and activity of glutathione synthase in response to deficiencies in folate, vitamin E, and apolipoprotein E

Oxidative stress is a major contributing factor in neurodegeneration and can arise from dietary, environmental, and genetic sources. Here we examine the separate and combined impact of deprivation of folate and vitamin E, coupled with dietary iron as a prooxidant, on normal mice and transgenic mice lacking apolipoprotein E (ApoE-/- mice). Both mouse strains exhibited increased levels of glutathione when deprived of folate and vitamin E, but a substantial further increase was observed in ApoE-/- mice. To determine the mechanism(s) underlying this increase, we quantified transcription and activity of glutathione synthase (GS). Both normal and ApoE-/- mice demonstrated increased GS activity when deprived of folate and vitamin E. However, transcription was increased only in ApoE-/- mice deprived of folate and vitamin E. These findings demonstrate that deficiency in one gene can result in compensatory up-regulation in a second relevant gene and, furthermore, indicate that compensation for oxidative stress can occur in brain tissue at epigenetic and genetic levels depending on the nature and/or extent of oxidative stress.

Folate deficiency and homocysteine induce toxicity in cultured dorsal root ganglion neurons via cytosolic calcium accumulation

Folate deficiency induces neurotoxicity by multiple routes, including increasing cytosolic calcium and oxidative stress via increasing levels of the neurotoxin homocysteine (HC), and inducing mitochondrial and DNA damage. Because some of these neurotoxic effects overlap with those observed in motor neuron disease, we examined the impact of folate deprivation on dorsal root ganglion (DRG) neurons in culture. Folate deprivation for 2 h increased cytosolic calcium and reactive oxygen species (ROS) and impaired mitochondrial function. Treatment with nimodipine [an L voltage-sensitive calcium channel (LVSCC) antagonist], MK-801 (an NMDA channel antagonist) and thapsigarin (an inhibitor of efflux of calcium from internal stores) indicated that folate deprivation initially induced calcium influx via the LVSCC, with subsequent additional calcium derived from NMDA channels and internal stores. These compounds also reduced ROS and mitochondrial degeneration, indicating that calcium influx contributed to these phenomena. Calcium influx was prevented by co-treatment with 3-deaza-adenosine, which inhibits HC formation, indicating that HC mediated increased cytosolic calcium following folate deprivation. Nimodipine, MK-801 and thapsigargin had similar effects following direct treatment with HC as they did following folate deprivation. These findings support the idea that folate deprivation and HC treatment can compromise the health of DRG neurons by perturbing calcium homeostasis.

Cell cycle activation linked to neuronal cell death initiated by DNA damage

Increasing evidence indicates that neurodegeneration involves the activation of the cell cycle machinery in postmitotic neurons. However, the purpose of these cell cycle-associated events in neuronal apoptosis remains unknown. Here we tested the hypothesis that cell cycle activation is a critical component of the DNA damage response in postmitotic neurons. Different genotoxic compounds (etoposide, methotrexate, and homocysteine) induced apoptosis accompanied by cell cycle reentry of terminally differentiated cortical neurons. In contrast, apoptosis initiated by stimuli that do not target DNA (staurosporine and colchicine) did not initiate cell cycle activation. Suppression of the function of ataxia telangiectasia mutated (ATM), a proximal component of DNA damage-induced cell cycle checkpoint pathways, attenuated both apoptosis and cell cycle reentry triggered by DNA damage but did not change the fate of neurons exposed to staurosporine and colchicine. Our data suggest that cell cycle activation is a critical element of the DNA damage response of postmitotic neurons leading to apoptosis.

20S proteasome mediated degradation of DHFR: implications in neurodegenerative disorders

The 20S proteasome is responsible for the degradation of protein substrates implicated in the onset and progression of neurodegenerative disorders, such as alpha-synuclein and tau protein. Here we show that the 20S proteasome isolated from bovine brain directly hydrolyzes, in vitro, the dihydrofolate reductase (DHFR), demonstrated to be involved in the pathogenesis of neurodegenerative diseases. Furthermore, the DHFR susceptibility to proteolysis is enhanced by oxidative conditions induced by peroxynitrite, mimicking the oxidative environment typical of these disorders. The results obtained suggest that the folate metabolism may be impaired by an increased degradation of DHFR, mediated by the 20S proteasome.

Folate and homocysteine interrelationships including genetics of the relevant enzymes

PURPOSE OF REVIEW

Inadequate folate status has been linked to risk of a wide range of adverse health conditions throughout life, from birth defects and complications of pregnancy to cardiovascular disease, cancer and cognitive dysfunction in the elderly. In many instances these risks are manifested through elevated plasma homocysteine. This review focuses on current research into the contribution of genetic variability to folate status and disease predisposition.

RECENT FINDINGS

Some dozen potentially important polymorphisms in folate-related genes have been examined for disease associations or for their role in determining the level of plasma homocysteine. In most instances, the effects are either modest, not significant, or undetectable. However, the mechanism by which the 677C-->T variant of methylenetetrahydrofolate reductase determines homocysteine status has become clearer with the elucidation of a critical role for riboflavin in modulating the plasma homocysteine of TT homozygotes. Moreover, several new metaanalyses have confirmed an association of this variant with vascular disease, probably through low folate status and elevated plasma homocysteine.

SUMMARY

There are enormous difficulties in attempting to assess the contribution of minor genetic variability to nutrient status, against major background differences due to ethnicity, age, gender, lifestyle, dietary habits and disease status. Nevertheless, this is an important goal in the future management of chronic multifactorial disease. The present research into the genetic components of folate and homocysteine variability is paving the way towards an eventual capacity to ensure optimal folate status in every individual and, consequently, to reduce their risk of developing such diseases.

Infectious agents and age-related neurodegenerative disorders

chlamdAs with other organ systems, the vulnerability of the nervous system to infectious agents increases with aging. Several different infectious agents can cause neurodegenerative conditions, with prominent examples being human immunodeficiency virus (HIV-1) dementia and prion disorders. Such infections of the central nervous system (CNS) typically have a relatively long incubation period and a chronic progressive course, and are therefore increasing in frequency as more people live longer. Infectious agents may enter the central nervous system in infected migratory macrophages, by transcytosis across blood-brain barrier cells or by intraneuronal transfer from peripheral nerves. Synapses and lipid rafts are important sites at which infectious agents may enter neurons and/or exert their cytotoxic effects. Recent findings suggest the possibility that infectious agents may increase the risk of common age-related neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS) and stroke. While scenarios can be envisioned whereby viruses such as Chlamydia pneumoniae, herpes simplex and influenza promote damage to neurons during aging, there is no conclusive evidence for a major role of these pathogens in neurodegenerative disorders. In the case of stroke, blood vessels may be adversely affected by bacteria or viruses resulting in atherosclerosis.

Utilization of Cognitive Support in Episodic Free Recall as a Function of Apolipoprotein E and Vitamin B₁₂ or Folate Among Adults Aged 75 Years and Older

Apolipoprotein E (APOE), vitamin B12, and folate were examined in relation to free recall among 167 community-based older adults. Cognitive support at encoding and retrieval was also taken into account. Participants were classified as APOE e4 or non-epsilon4 allele carriers and as either low or normal vitamin B12 or folate status. A significant association was identified between low vitamin B12 and the epsilon4 genotype in respect to free recall, but only in circumstances of low cognitive support. This result remained after removing dementia cases that occurred up to 6 years after testing. A similar, but nonsignificant, trend was evident in relation to folate. The research is discussed with reference to vulnerability models and genetic influences on brain reserves.

Increased homocysteine levels associated with sex and stress in the learned helplessness model of depression

Elevated levels of homocysteine (Hcy) have been associated with major depressive (MD) illness. As human females show a higher predisposition towards depression, this study examined how Hcy levels in rats are affected by sex and estrous cycle in the learned helplessness (LH) model of depression. Male and female rats in either estrus or diestrus were subjected to LH, with intervals of 4 days between the two stress tests and between tests and sacrifice, in order to accommodate the female estrous cycle. No differences were found in LH behavior between males and females at either estrous phase. Control Hcy levels were significantly lower in females than in males (-36%, P<.001), with no further differences between estrous and diestrus phases in females. Stress exposure increased plasma Hcy by approximately 26% in females, both in estrus and diestrus, but not in males. However, when behavioral responses to stress were considered, no association was found between increased Hcy levels and propensity to develop helpless behavior. Therefore, while male rats have higher basal Hcy levels than females, females appear to be more vulnerable than males to stress-induced elevations in Hcy, although this did not correlate with behavioral responses to stress. Neither was this vulnerability influenced by estrous phase. These results imply that both stress and sex should be considered as risk factors for increased plasma Hcy.

The dominant role of Sp1 in regulating the cystathionine beta-synthase -1a and -1b promoters facilitates potential tissue-specific regulation by Kruppel-like factors

Cystathionine beta-synthase (CBS) catalyzes the condensation of serine with homocysteine to form cystathionine and occupies a crucial regulatory position between the methionine cycle and transsulfuration. The human cystathionine beta-synthase gene promoters -1a and -1b are expressed in a limited number of tissues and are coordinately regulated with proliferation through a redox-sensitive mechanism. Site-directed mutagenesis, DNase I footprinting and deletion analysis of 5276 bp of 5' proximal -1b flanking sequence revealed that this region does not confer tissue-specific expression and that 210 bp of proximal sequence is sufficient for maximal promoter activity. As little as 32 bp of the -1b proximal promoter region is capable of driving transcription in HepG2 cells, and this activity is entirely dependent upon the presence of a single overlapping Sp1/Egr1 binding site. Co-transfection studies in Drosophila SL2 cells indicated that both promoters are transactivated by Sp1 and Sp3 but only the -1b promoter is subject to a site-specific synergistic regulatory interaction between Sp1 and Sp3. Sp1-deficient fibroblasts expressing both Sp3 and NF-Y were negative for CBS activity. Transfection of these cells with a mammalian Sp1 expression construct induced high levels of CBS activity indicating that Sp1 has a critical and indispensable role in the regulation of cystathionine beta-synthase. Sp1 binding to both CBS promoters is sensitive to proliferation status and is negatively regulated by Kruppel-like factors in co-transfection experiments suggesting a possible mechanism for the tissue specific regulation of cystathionine beta-synthase.

The role of cardiovascular risk factors in Alzheimer's disease

The distinction between Alzheimer's disease and vascular dementia, the two most common types of dementia, has been undermined by recent advances in epidemiologic, clinical, imaging, and neuropathological studies. Cardiovascular risk factors, traditionally regarded as distinguishing criteria between the two entities, have been shown to be associated with both AD and vascular dementia. In this article, we propose mechanisms of action of cardiovascular risk factors in AD, suggest possible explanations for the overlap with vascular dementia and discuss the implications this might have on future differential diagnosis, research, and treatment strategies.

Emerging therapeutics for Alzheimer's disease: an avenue of hope

Emerging therapies for Alzheimer's disease offer hope to patients and their caregivers. Future treatments will probably include combination approaches with agents that modify amyloid processing, deposition, and clearance. One example, the AD vaccine, reduced amyloid burden and changed behavior in animal models of AD, but the human trial was halted when several subjects developed brain inflammation. Anti-inflammatory agents have epidemiologic support, but clinical trials have been disappointing, possibly related to inadequate study with anti-inflammatory agents that modify amyloid processing. Agents that target known cardiovascular risk factors, such as hypercholesterolemia, hypertension, and insulin resistance, have epidemiologic, preclinical, and clinical evidence to warrant further investigation. Heavy metal chelators, antioxidants, neurotrophic factors, glutaminergic modulators, and agents that modify hyperphosphorylation of Tau are other approaches in research and development.

Neuronal and glial calcium signaling in Alzheimer's disease

Cognitive impairment and emotional disturbances in Alzheimer's disease (AD) result from the degeneration of synapses and death of neurons in the limbic system and associated regions of the cerebral cortex. An alteration in the proteolytic processing of the amyloid precursor protein (APP) results in increased production and accumulation of amyloid beta-peptide (Abeta) in the brain. Abeta has been shown to cause synaptic dysfunction and can render neurons vulnerable to excitotoxicity and apoptosis by a mechanism involving disruption of cellular calcium homeostasis. By inducing membrane lipid peroxidation and generation of the aldehyde 4-hydroxynonenal, Abeta impairs the function of membrane ion-motive ATPases and glucose and glutamate transporters, and can enhance calcium influx through voltage-dependent and ligand-gated calcium channels. Reduced levels of a secreted form of APP which normally regulates synaptic plasticity and cell survival may also promote disruption of synaptic calcium homeostasis in AD. Some cases of inherited AD are caused by mutations in presenilins 1 and 2 which perturb endoplasmic reticulum (ER) calcium homeostasis such that greater amounts of calcium are released upon stimulation, possibly as the result of alterations in IP(3) and ryanodine receptor channels, Ca(2+)-ATPases and the ER stress protein Herp. Abnormalities in calcium regulation in astrocytes, oligodendrocytes, and microglia have also been documented in studies of experimental models of AD, suggesting contributions of these alterations to neuronal dysfunction and cell death in AD. Collectively, the available data show that perturbed cellular calcium homeostasis plays a prominent role in the pathogenesis of AD, suggesting potential benefits of preventative and therapeutic strategies that stabilize cellular calcium homeostasis.

Role of group I metabotropic glutamate receptors and NMDA receptors in homocysteine-evoked acute neurodegeneration of cultured cerebellar granule neurones

Hyperhomocysteinemia is a risk factor in neurodegeneration. It has been suggested that apart from disturbances in methylation processes, the mechanisms of this effect may include excitotoxicity mediated by the N-methyl-D-aspartate (NMDA) receptors. In this study we demonstrate that apart from NMDA receptors, also group I metabotropic glutamate receptors participate in acute homocysteine (Hcy)-induced neurotoxicity in cultured rat cerebellar granule neurones. Primary neuronal cultures were incubated for 30 min in the Mg(2+)-free ionic medium containing homocysteine and other ligands, and neurodegenerative changes were assessed 24h later using propidium iodide staining. D,L-Homocysteine given alone appeared to be a weak neurotoxin, with EC(50) of 17.4mM, whereas EC(50) for L-glutamate was 0.17 mM. Addition of 50 microM glycine enhanced homocysteine neurotoxicity, and only that portion of neurotoxicity was abolished by 0.5 microM MK-801, an uncompetitive NMDA receptor antagonist. The net stimulation of 45Ca uptake by granule cells incubated in the presence of 25 mM D,L-homocysteine with 50 microM glycine was only 3% of the net uptake evoked by 1mM glutamate. Application of an antagonist of group I metabotropic glutamate receptors (mGluRs) LY367385 at 25 and 250 microM concentrations, induced a dose-dependent partial neuroprotection, whereas given together with MK-801 completely prevented neurotoxicity. In the absence of glycine, LY367385 and MK-801 given alone failed to induce neuroprotection, while applied together completely prevented homocysteine neurotoxicity. Agonist of group I mGluRs, 10 trans-azetidine-2,3-dicarboxylic acid (t-ADA) induced significant neurotoxicity. This study shows for the first time that acute homocysteine-induced neurotoxicity is mediated both by group I mGluRs and NMDA receptors, and is not accompanied by massive influx of extracellular Ca(2+) to neurones.

Homocysteine and Alzheimer's disease

BACKGROUND

A high circulating concentration of the amino acid homocysteine is an independent risk factor for stroke. Alzheimer's disease (AD) commonly co-occurs with stroke. Epidemiological studies found associations between hyperhomocysteinaemia and both histologically confirmed AD and disease progression and revealed that dementia in AD was associated with evidence of brain infarcts on autopsy. Thus, hyperhomocysteinaemia and AD could be linked by stroke or microvascular disease. However, given known relations between B-group-vitamin deficiency and both hyperhomocysteinaemia and neurological dysfunction, direct causal mechanisms are also plausible.

RECENT DEVELOPMENTS

A recent prospective study (S Seshadri and colleagues N Engl J Med; 2002 346: 476-83) showed hyperhomocysteinaemia to be a strong, independent risk factor for dementia and AD. The researchers found a graded increase in risk of both outcomes with rising plasma concentration of homocysteine after multivariate control for putative risk factors for AD. In conjunction with demonstration of a fall in homocysteine concentrations in response to increasing B-group-vitamin status, these findings give hope that mental decline, or AD itself, could be prevented by dietary modification or food fortification. WHERE NEXT? 25% of dementia cases are attributed to stroke. The possibility that some of the other 75% might be prevented by the lowering of homocysteine concentrations greatly increases the hope of maintaining self-sufficiency into old age. If homocysteine lowering can reduce the incidence of dementia or AD, decreased incidence of these disorders may be seen in Canada and the USA, where government-mandated folate-fortification programmes are in effect. Future research should focus on early detection of AD and on the possibility that the disease itself, or its primary symptom, could be prevented by folate supplementation.

Methylation and acetylation in nervous system development and neurodegenerative disorders

The cytoarchitecture and cellular signaling mechanisms of the nervous system are complex, and this complexity is reflected at the molecular level with more genes being expressed in the nervous system than in any other tissue. Gene expression and protein function in neural cells can be regulated by methylation and acetylation. Studies of mice deficient in enzymes that control DNA methylation and of animals with a dietary deficiency of folate have established critical roles for methylation in development of the nervous system. Various neuronal proteins including histones and tubulin are regulated by acetylation which appears to serve important functions in the development, stability and plasticity of neuronal networks. Some inherited neurological disorders have recently been linked to mutations in genes that regulate DNA methylation, and alterations in DNA and protein methylation and/or acetylation have been documented in studies of age-related neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD). Manipulations of methylation and acetylation can affect the vulnerability of neurons to degeneration and apoptosis in experimental models of neurodegenerative disorders, suggesting a contribution to altered methylation and acetylation to the disease processes. Interestingly, dietary factors that influence DNA methylation may affect the risk of neurodegenerative disorders, for example, individuals with low dietary folate intake are at increased risk of Alzheimer's and Parkinson's diseases.

Impact of aging on DNA methylation

The biochemistry of aging is complex, with biologically significant changes occurring in proteins, lipids and nucleic acids. One of these changes is in the methylation of DNA. DNA methylation is a mechanism modifying gene expression. The methylation of sequences in or near regulatory elements can suppress gene expression through effects on DNA binding proteins and chromatin structure. Both increases and decreases in methylation occur with aging, depending on the tissue and the gene. These changes can have pathologic consequences, contributing to the development of malignancies and autoimmunity with aging, and possibly to other disorders as well. Thus, while aging can impact on DNA methylation, the changes in DNA methylation can also impact on aging. This review summarizes current evidence for changes in the methylation status of specific genes with aging, their impact on diseases that develop with aging, and mechanisms that may contribute to the altered DNA methylation patterns. As this field is still developing, it is anticipated that new knowledge will continue to accumulate rapidly.

Aging as war between chemical and biochemical processes: protein methylation and the recognition of age-damaged proteins for repair

Deamidated, isomerized, and racemized aspartyl and asparaginyl residues represent a significant part of the spontaneous damage to proteins that results from the aging process. The accumulation of these altered residues can lead to the loss of protein function and the consequent loss of cellular function. However, almost all cells in nature contain a methyltransferase that can recognize the major damaged form of the L-isoaspartyl residue, and some of these enzymes can also recognize the racemized D-aspartyl residue. The methyl esterification reaction can initiate the conversion of these altered residues to the normal L-aspartyl form, although there is no evidence yet that the L-asparaginyl form can be regenerated. This enzyme, the protein L-isoaspartate (D-aspartate) O-methyltransferase (EC 2.1.1.77), thus functions as a protein repair enzyme. The importance of this enzyme in attenuating age-related protein damage can be seen by the phenotypes of organisms where the gene encoding has been disrupted, or where its expression has been augmented.

Plasma vitamin C, cholesterol and homocysteine are associated with grey matter volume determined by MRI in non-demented old people

We studied 82 non-demented old people and, using MRI, derived measures of grey and white matter and intracranial volumes. Controlling for sex and intracranial volume, we related grey and white matter volumes to plasma concentrations of vitamins C, B(12), folate, homocysteine, cholesterol, triglycerides, high density and low density (LDL) lipoproteins, and to red blood cell folate and glycated haemoglobin concentrations (HbA1(c)). We found that lower grey matter volume was associated with lower plasma vitamin C and higher homocysteine, cholesterol and LDL. Lower blood cell folate was also associated with lower grey matter volume but HbA1(c) was not. These data are consistent with the putative benefits of dietary vitamin C and folate intake and the role of cholesterol in age related neurodegeneration.

Pathology and pathways of Alzheimer's disease with an update on new developments in treatment

As our understanding of the complex pathology of Alzheimer's disease improves, more targets for therapy emerge. These include the actions of beta amyloid, the inflammatory cascade, pathobiology of tau proteins' conversion to neurofibrillary tangles, oxidative neuronal damage, and neurotransmitter depletion. Many agents now under investigation target the early stages of the disease process, aiming to prevent or slow the development of symptoms. This article reviews the current understanding of the course and pathology of Alzheimer's disease as it relates to emerging therapies, then summarizes some promising current research directions in primary prevention, secondary prevention, and treatment.

Is the distinction between Alzheimer's disease and vascular dementia possible and relevant?

Advances in epidemiological, clinical, imaging, and neuropathological studies have undermined the clear distinction between vascular and Alzheimer-type dementia, which has characterized the last two decades of research in dementia. A significant degree of overlap between the two entities was demonstrated in terms of clinical expression, risk factors, and postmortem brain autopsy. In this article, we propose mechanisms by which cardiovascular risk factors might affect the manifestation of Alzheimer's disease, suggest possible explanations for the overlap with vascular dementia, and discuss the implications this might have on future differential diagnosis and treatment strategies.

Immunohistochemical study on the distribution of homocysteine in the central nervous system of transgenic mice expressing a human Cu/Zn SOD mutation

In the present study, we used the transgenic mice expressing a human Cu/Zn SOD mutation (SOD1(G93A)) as an in vivo model of ALS and performed immunohistochemical studies to investigate the changes of homocysteine in the central nervous system of symptomatic transgenic mice. In control and presymptomatic transgenic mice, homocysteine-immunoreactive astrocytes were not detected in any region. In symptomatic transgenic mice, homocysteine-immunoreactive astrocytes were distributed in the spinal cord, brainstem and cerebellar nuclei of transgenic mice. In the hippocampal formation of transgenic mice, pyramidal cells in the CA1-3 regions and granule cells in the dentate gyrus showed homocysteine immunoreactivity. The present study provides the first in vivo evidence that homocysteine immunoreactive astrocytes were found in the central nervous system of symptomatic SOD(G93A) transgenic mice, suggesting that reactive astrocytes may play an important role in the pathogenesis and progress of ALS. This study also suggests that increased expression of homocysteine in the hippocampal neurons might reflect a role of homocysteine in an abnormality of hippocampal function of ALS.