Oxidative Stress in Alzheimer’s Disease: Why Did Antioxidant Therapy Fail?

Alzheimer’s disease (AD) is the most common form of dementia in the elderly, with increasing prevalence and no disease-modifying treatment available yet. A remarkable amount of data supports the hypothesis that oxidative stress is an early and important pathogenic operator in AD. However, all clinical studies conducted to date did not prove a clear beneficial effect of antioxidant treatment in AD patients. In the current work, we review the current knowledge about oxidative stress in AD pathogeny and we suggest future paths that are worth to be explored in animal models and clinical studies, in order to get a better approach of oxidative imbalance in this inexorable neurodegenerative disease

Age-dependent pharmacokinetics and effect of roscovitine on Cdk5 and Erk1/2 in the rat brain.

Roscovitine is a cyclin-dependent kinase (Cdk) and signal-regulated kinase (Erk1/2) inhibitor that has been shown to be effective against several cancer types including brain tumors. We have shown previously that roscovitine crosses the blood brain barrier (BBB) and is rapidly eliminated from both plasma and brain in adult rats. However, age-dependent kinetics and its effects on the brain have not been reported. In the present study, we investigated the pharmacokinetics of roscovitine in adult and in 14 days old rats after the administration of a single dose of 25 mg/kg. Moreover, we studied the effect of the drug on Cdk5 and Erk1/2 activities in three brain regions, hippocampus, frontal cortex and cerebellum. The pharmacokinetics of roscovitine followed a two-compartment model in both plasma and brain in both adult and young rats. The terminal elimination half-life was 7 h in brain as well as in plasma in rat pups compared to < 0.5 h observed in adult rats. Brain exposure expressed as AUC brain/AUC plasma was 100% in rat pups compared to 20% found in adult rats. Roscovitine induced a significant Cdk5 inhibition and significant Erk1/2 activation in all studied pups brain regions at 2 h. This is the first study describing age-dependent pharmacokinetics of roscovitine and showing the high brain exposure of infant rats to the drug. Thus, roscovitine may be a promising candidate for the treatment of brain tumors in children

Анализ вероятностных моделей параметрических правил принятия решений функциональной диагностики

Рассмотрена задача статистического обоснования выбора вида математической модели измерительно-логических преобразований для процедуры функциональной диагностики с учетом ограниченности априорной информации о свойствах объекта диагностики. Построена и проанализирована информационная модель процедуры диагностики, которая учитывает требования плана диагностического эксперимента и вероятностные свойства математической модели этой процедуры.The problem of statistical justification of selecting the type of the mathematical model of measuring-logical transformations for the procedure of functional diagnostics taking into account limited aprioristic information on the properties of the object of diagnostics is considered. An information model of the procedure of diagnostics taking into account the requirements of the plan of diagnostics experiment and probabilistic properties of the mathematical model of this procedure is built and analyzed

Cholesterol 24S-Hydroxylase overexpression inhibits the liver X receptor (LXR) pathway by activating small guanosine triphosphate-binding proteins (sGTPases) in neuronal cells

The neuronal-specific cholesterol 24S-hydroxylase (CYP46A1) is important for brain cholesterol elimination. Cyp46a1 null mice exhibit severe deficiencies in learning and hippocampal long-term potentiation, suggested to be caused by a decrease in isoprenoid intermediates of the mevalonate pathway. Conversely, transgenic mice overexpressing CYP46A1 show an improved cognitive function. These results raised the question of whether CYP46A1 expression can modulate the activity of proteins that are crucial for neuronal function, namely of isoprenylated small guanosine triphosphate-binding proteins (sGTPases). Our results show that CYP46A1 overexpression in SH-SY5Y neuroblastoma cells and in primary cultures of rat cortical neurons leads to an increase in 3-hydroxy-3-methyl-glutaryl-CoA reductase activity and to an overall increase in membrane levels of RhoA, Rac1, Cdc42 and Rab8. This increase is accompanied by a specific increase in RhoA activation. Interestingly, treatment with lovastatin or a geranylgeranyltransferase-I inhibitor abolished the CYP46A1 effect. The CYP46A1-mediated increase in sGTPases membrane abundance was confirmed in vivo, in membrane fractions obtained from transgenic mice overexpressing this enzyme. Moreover, CYP46A1 overexpression leads to a decrease in the liver X receptor (LXR) transcriptional activity and in the mRNA levels of ATP-binding cassette transporter 1, sub-family A, member 1 and apolipoprotein E. This effect was abolished by inhibition of prenylation or by co-transfection of a RhoA dominant-negative mutant. Our results suggest a novel regulatory axis in neurons; under conditions of membrane cholesterol reduction by increased CYP46A1 expression, neurons increase isoprenoid synthesis and sGTPase prenylation. This leads to a reduction in LXR activity, and consequently to a decrease in the expression of LXR target genes

Neuronal cholesterol metabolism increases dendritic outgrowth and synaptic markers via a concerted action of GGTase-I and Trk

We are deeply thankful to Professor David W. Russell (University of Texas Southwestern Medical Center) for the kind gift of the anti-CYP46A1 antibody. This work was supported by FEDER (COMPETE Programme) and national funds from Fundacao para a Ciencia e a Tecnologia (FCT), Portugal, research grants iMed.ULisboa (UID/DTP/04138/2013), PTDC/SAU/NMC/110809/2009 (to E.R.), SFRH/BD/78041/2011 (to M.M.) SFRH/BPD/95855/2013 (to M.J.N), and, Swedish Research Council (J.L.R. and I.B.), Marie Curie Career Integration Grant and Novo Nordisk Fonden (J.L.R.) and Swedish Brain Power (I.B.).Cholesterol 24-hydroxylase (CYP46A1) is responsible for brain cholesterol elimination and therefore plays a crucial role in the control of brain cholesterol homeostasis. Altered CYP46A1 expression has been associated with several neurodegenerative diseases and changes in cognition. Since CYP46A1 activates small guanosine triphosphate-binding proteins (sGTPases), we hypothesized that CYP46A1 might be affecting neuronal development and function by activating tropomyosin-related kinase (Trk) receptors and promoting geranylgeranyl transferase-I (GGTase-I) prenylation activity. Our results show that CYP46A1 triggers an increase in neuronal dendritic outgrowth and dendritic protrusion density, and elicits an increase of synaptic proteins in the crude synaptosomal fraction. Strikingly, all of these effects are abolished by pharmacological inhibition of GGTase-I activity. Furthermore, CYP46A1 increases Trk phosphorylation, its interaction with GGTase-I, and the activity of GGTase-I, which is crucial for the enhanced dendritic outgrowth. Cholesterol supplementation studies indicate that cholesterol reduction by CYP46A1 is the necessary trigger for these effects. These results were confirmed in vivo, with a significant increase of p-Trk, pre- and postsynaptic proteins, Rac1, and decreased cholesterol levels, in crude synaptosomal fractions prepared from CYP46A1 transgenic mouse cortex. This work describes the molecular mechanisms by which neuronal cholesterol metabolism effectively modulates neuronal outgrowth and synaptic markers.publishersversionpublishe

27-Hydroxycholesterol, cognition, and brain imaging markers in the FINGER randomized controlled trial

Background: 27-Hydroxycholesterol (27-OH), the main circulating oxysterol in humans and the potential missing link between peripheral hypercholesterolemia and Alzheimer's disease (AD), has not been investigated previously in relation to cognition and neuroimaging markers in the context of preventive interventions.Methods: The 2-year Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability (FINGER) included older individuals (60-77 years) at increased risk for dementia but without dementia or substantial cognitive impairment from the general population. Participants were randomized to a multidomain intervention (diet, exercise, cognitive training, and vascular risk management) or control group (general health advice) in a 1:1 ratio. Outcome assessors were masked to group allocation. This FINGER exploratory sub-study included 47 participants with measures of 27-OH, cognition, brain MRI, brain FDG-PET, and PiB-PET. Linear regression models were used to assess the cross-sectional and longitudinal associations between 27-OH, cognition, and neuroimaging markers, considering several potential confounders/intervention effect modifiers.Results: 27-OH reduction during the intervention was associated with improvement in cognition (especially memory). This was not observed in the control group. The intervention reduced 27-OH particularly in individuals with the highest 27-OH levels and younger age. No associations were found between changes in 27-OH levels and neuroimaging markers. However, at baseline, a higher 27-OH was associated with lower total gray matter and hippocampal volume, and lower cognitive scores. These associations were unaffected by total cholesterol levels. While sex seemed to influence associations at baseline, it did not affect longitudinal associations.Conclusion: 27-OH appears to be a marker not only for dementia/AD risk, but also for monitoring the effects of preventive interventions on cholesterol metabolism

Is it possible to improve memory function by upregulation of the cholesterol 24S-hydroxylase (CYP46A1) in the brain? PLoS One

Abstract We previously described a heterozygous mouse model overexpressing human HA-tagged 24S-hydroxylase (CYP46A1) utilizing a ubiquitous expression vector. In this study, we generated homozygotes of these mice with circulating levels of 24OH 30-60% higher than the heterozygotes. Female homozygous CYP46A1 transgenic mice, aged 15 months, showed an improvement in spatial memory in the Morris water maze test as compared to the wild type mice. The levels of N-Methyl-DAspartate receptor 1, phosphorylated-N-Methyl-D-Aspartate receptor 2A, postsynaptic density 95, synapsin-1 and synapthophysin were significantly increased in the hippocampus of the CYP46A1 transgenic mice as compared to the controls. The levels of lanosterol in the brain of the CYP46A1 transgenic mice were significantly increased, consistent with a higher synthesis of cholesterol. Our results are discussed in relation to the hypothesis that the flux in the mevalonate pathway in the brain is of importance in cognitive functions

24(S),25-Epoxycholesterol and cholesterol 24S-hydroxylase (CYP46A1) overexpression promote midbrain dopaminergic neurogenesis in vivo

The liver X receptors Lxrα/NR1H3 and Lxrβ/NR1H2 are ligand-dependent nuclear receptors critical for midbrain dopaminergic (mDA) neuron development. We previously found that 24(S),25-epoxycholesterol (24,25-EC), the most potent and abundant Lxr ligand in the developing mouse midbrain, promotes mDA neurogenesis in vitro. In this study, we demonstrate that 24,25-EC promotes mDA neurogenesis in an Lxr-dependent manner, in the developing mouse midbrain in vivo and also prevents toxicity induced by the Lxr inhibitor geranylgeranyl pyrophosphate. Furthermore, using MS we show that overexpression of human cholesterol 24S-hydroxylase (CYP46A1) increases the levels of both 24(S)-hydroxycholesterol (24-HC) and 24,25-EC in the developing midbrain, resulting in a specific increase in mDA neurogenesis in vitro and in vivo, but has no effect on occulomotor or red nucleus neurogenesis. 24-HC, unlike 24,25-EC, did not affect in vitro neurogenesis, indicating that the neurogenic effect of 24,25-EC on mDA neurons is specific. Combined, our results indicate that increased levels of 24,25-EC in vivo, by intracerebroventricular delivery in wild-type mice or by overexpression of its biosynthetic enzyme CYP46A1, specifically promote mDA neurogenesis. We propose that increasing the levels of 24,25-EC in vivo may be a useful strategy to combat the loss of mDA neurons in Parkinson’s disease

Alzheimer's disease biomarker profiling in a memory clinic cohort without common comorbidities

Alzheimer's disease is a multifactorial disorder with large heterogeneity. Comorbidities such as hypertension, hypercholesterolaemia and diabetes are known contributors to disease progression. However, less is known about their mechanistic contribution to Alzheimer's pathology and neurodegeneration. The aim of this study was to investigate the relationship of several biomarkers related to risk mechanisms in Alzheimer's disease with the well-established Alzheimer's disease markers in a memory clinic population without common comorbidities. We investigated 13 molecular markers representing key mechanisms underlying Alzheimer's disease pathogenesis in CSF from memory clinic patients without diagnosed hypertension, hypercholesterolaemia or diabetes nor other neurodegenerative disorders. An analysis of covariance was used to compare biomarker levels between clinical groups. Associations were analysed by linear regression. Two-step cluster analysis was used to determine patient clusters. Two key markers were analysed by immunofluorescence staining in the hippocampus of non-demented control and Alzheimer's disease individuals. CSF samples from a total of 90 participants were included in this study: 30 from patients with subjective cognitive decline (age 62.4 ± 4.38, female 60%), 30 with mild cognitive impairment (age 65.6 ± 7.48, female 50%) and 30 with Alzheimer's disease (age 68.2 ± 7.86, female 50%). Angiotensinogen, thioredoxin-1 and interleukin-15 had the most prominent associations with Alzheimer's disease pathology, synaptic and axonal damage markers. Synaptosomal-associated protein 25 kDa and neurofilament light chain were increased in mild cognitive impairment and Alzheimer's disease patients. Grouping biomarkers by biological function showed that inflammatory and survival components were associated with Alzheimer's disease pathology, synaptic dysfunction and axonal damage. Moreover, a vascular/metabolic component was associated with synaptic dysfunction. In the data-driven analysis, two patient clusters were identified: Cluster 1 had increased CSF markers of oxidative stress, vascular pathology and neuroinflammation and was characterized by elevated synaptic and axonal damage, compared with Cluster 2. Clinical groups were evenly distributed between the clusters. An analysis of post-mortem hippocampal tissue showed that compared with non-demented controls, angiotensinogen staining was higher in Alzheimer's disease and co-localized with phosphorylated-tau. The identification of biomarker-driven endophenotypes in cognitive disorder patients further highlights the biological heterogeneity of Alzheimer's disease and the importance of tailored prevention and treatment strategies

Insulin-Independent and Dependent Glucose Transporters in Brain Mural Cells in CADASIL

Typical cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is caused by mutations in the human NOTCH3 gene. Cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy is characterized by subcortical ischemic strokes due to severe arteriopathy and fibrotic thickening of small vessels. Blood regulating vascular smooth muscle cells (VSMCs) appear as the key target in CADASIL but the pathogenic mechanisms remain unclear. With the hypothesis that brain glucose metabolism is disrupted in VSMCs in CADASIL, we investigated post-mortem tissues and VSMCs derived from CADASIL patients to explore gene expression and protein immunoreactivity of glucose transporters (GLUTs), particularly GLUT4 and GLUT2 using quantitative RT-PCR and immunohistochemical techniques.In vitrocell model analysis indicated that both GLUT4 and -2 gene expression levels were down-regulated in VSMCs derived from CADASIL patients, compared to controls.In vitrostudies further indicated that the down regulation of GLUT4 coincided with impaired glucose uptake in VSMCs, which could be partially rescued by insulin treatment. Our observations on reduction in GLUTs in VSMCs are consistent with previous findings of decreased cerebral blood flow and glucose uptake in CADASIL patients. That impaired ability of glucose uptake is rescued by insulin is also consistent with previously reported lower proliferation rates of VSMCs derived from CADASIL subjects. Overall, these observations are consistent with the development of severe cerebral arteriopathy in CADASIL, in which VSMCs are replaced by widespread fibrosis