Essays Biochem

Energy metabolism is essential for brain function. In recent years, lactate shuttling between astrocytes and neurons has become a fundamental concept of neuroenergetics. However, it remains unclear to what extent this process is critical for different aspects of cognition, their underlying mechanisms, as well as for the signals used to monitor brain activation.Rôle des différents substrats énergétiques pour l'activité cérébral

Catecholamines and cognition after traumatic brain injury

Cognitive problems are one of the main causes of ongoing disability after traumatic brain injury. The heterogeneity of the injuries sustained and the variability of the resulting cognitive deficits makes treating these problems difficult. Identifying the underlying pathology allows a targeted treatment approach aimed at cognitive enhancement. For example, damage to neuromodulatory neurotransmitter systems is common after traumatic brain injury and is an important cause of cognitive impairment. Here, we discuss the evidence implicating disruption of the catecholamines (dopamine and noradrenaline) and review the efficacy of catecholaminergic drugs in treating post-traumatic brain injury cognitive impairments. The response to these therapies is often variable, a likely consequence of the heterogeneous patterns of injury as well as a non-linear relationship between catecholamine levels and cognitive functions. This individual variability means that measuring the structure and function of a person’s catecholaminergic systems is likely to allow more refined therapy. Advanced structural and molecular imaging techniques offer the potential to identify disruption to the catecholaminergic systems and to provide a direct measure of catecholamine levels. In addition, measures of structural and functional connectivity can be used to identify common patterns of injury and to measure the functioning of brain ‘networks’ that are important for normal cognitive functioning. As the catecholamine systems modulate these cognitive networks, these measures could potentially be used to stratify treatment selection and monitor response to treatment in a more sophisticated manner

Exploring the Impact of Decreased AMPK Pathway Activity on Brain Injury Outcome

Each year, 150 million people sustain a Traumatic Brain Injury (TBI). TBI results in life-long cognitive impairments for many survivors. One observed pathological alteration following TBI are changes in glucose metabolism. Altered glucose uptake occurs in the periphery as well as in the nervous system, with an acute increase in glucose uptake, followed by a prolonged metabolic suppression. Chronic, persistent suppression of brain glucose uptake occurs in TBI patients experiencing memory loss. Abberant post-injury activation of energy-sensing signaling cascades could result in perturbed cellular metabolism. AMP-activated kinase (AMPK) is a kinase that senses low ATP levels, and promotes efficient cell energy usage. AMPK promotes energy production through increasing glucose uptake via glucose transporter 4 (GLUT4). When AMPK is activated, it phosphorylates Akt Substrate of 160 kDa (AS160), a Rab GTPase activating protein that controls Glut4 translocation. Additionally, AMPK negatively regulates energy-consumption by inhibiting protein synthesis via the mechanistic Target of Rapamycin (mTOR) pathway. Given that metabolic suppression has been observed post-injury, we hypothesized that activity of the AMPK pathway is transiently decreased. As AMPK activation increases energy efficiency of the cell, we proposed that increasing AMPK activity to combat the post-injury energy crisis would improve cognitive outcome. Additionally, we expected that inhibiting AMPK targets would be detrimental. We first investigated the role of an existing state of hyperglycemia on TBI outcome, as hyperglycemia correlates with increased mortality and decreased cognitive outcome in clinical studies. Inducing hyperglycemia had no effect on outcome; however, we discovered that AMPK and AS160 phosphorylation were altered post-injury. We conducted vii work to characterize this period of AMPK suppression and found that AMPK phosphorylation was significantly decreased in the hippocampus and cortex between 24 hours and 3 days post-injury, and phosphorylation of its downstream targets was consistently altered. Based on this period of observed decreased AMPK activity, we administered an AMPK activator post-injury, and this improved cognitive outcome. Finally, to examine whether AMPK-regulated target Glut4 is involved in post-injury glucose metabolism, we applied an inhibitor and found this treatment impaired post-injury cognitive function. This work is significant, as AMPK activation may represent a new TBI therapeutic target

Development of a Multimodal MRI Study to Characterize Morpho-Functional Features in Rodent Models of Alzheimer's Disease

Alzheimer’s Disease (AD) is the most common form of dementia, recognized by the World Health Organization as a global public health priority. It is a complex pathology characterized by the accumulation of the Amyloid-β (Aβ) peptide as extracellular plaques and of the intracellullar neuro fibrillary tangles (NFT) alongside with different events, such as chronic neuroinflammation and astrogliosis. None of the existing biomarkers is simultaneously specific for the pathology and sensitive to its progression. Metabolic and functional alterations are the earliest events described in the AD pathological cascade but shared with other form of dementia, while specific structural alterations occurs in a later stage of the disease. The use of transgenic models could simplify the development of new imaging biomarkers that would enable early diagnosis and making new treatments more effective. The objective of this work was to develop a multi-modal panel of magnetic resonance imaging (MRI) techniques and automated analysis pipelines, characterized by a high translational impact, in order to investigate the metabolic, functional and structural alterations in the brains of AD transgenic models. Results obtained in the APP23 transgenic mouse show that chemical exchange saturation transfer (CEST) imaging can be used to detect alterations in the brain uptake of the glucose analogue 2-deoxy-d-glucose (2DG) with a better resolution than PET and without the need of radioactive tracers. Moreover, a longitudinal study highlighted that significant structural and metabolic alterations can be found only in a late stage of the pathology. Furthermore, an advanced pipeline for the analysis of the rodent brain functional connectivity has been developed. This thesis demonstrates that the advantage to the experimental design adopted is simplifying longitudinal studies of the same animal cohort. The translation of the analysis pipelines adopted in human studies enables more powerful results and reduces the number of animals involved in research

Measuring NMDA receptors in vivo using [¹⁸F]GE-179 PET in health and disease

Background: N-methyl-D-aspartate receptors (NMDAR) are important glutamatergic ion channels in the brain. Studying the functional activation of NMDAR in vivo in humans has not been possible until recently. / Methods: We used positron emission tomography (PET) with [18F]GE-179, a novel radioligand binding inside the open NMDAR channel, to assess the in vivo activation of NMDAR. We developed methodology for quantification of ligand binding (Project 1) that did not require arterial sampling and was then applied to study NMDAR activation in aging (n=29, Project 2), epilepsy (n=26, Project 3), and Anti-NMDAR encephalitis (n=5, Project 4). / Results: In Project 1, we validated a method for kinetic modelling using an imagederived input function and serial venous samples. This approach provided unbiased estimates of ligand volume of distribution (VT) that were highly correlated (r=0.95, p<0.001) with the gold standard, an arterial input function. In Project 2, we observed increased tracer uptake related to aging in healthy individuals (VT increase of 0.6 per 10 years, p=0.04), particularly in bilateral hippocampi, temporo-parieto-occipital junctions, dorsolateral prefrontal cortex, and striata. In people with epilepsy, the age-related increase in VT (1.4 per 10 years, p=0.006) was most pronounced in the striatum and thalamus. In Project 3, we found reduced interictal ligand uptake in epilepsy that was related to longer disease duration (VT decrease of 1.6 per 10 years, p=0.004), spatially widespread and bihemispheric. Regional uptake was increased in those taking lacosamide and after anterior temporal lobe resection. In Project 4, we observed decreased ligand uptake in Anti-NMDAR encephalitis with persisting Anti-GluN1-antibodies (mean VT 6.2 in cases vs. 8.8 in healthy volunteers, p=0.02), particularly in bilateral anterior temporal and superior parietal lobes. / Conclusions: [18F]GE-179 PET is useful to detect altered NMDAR function. We observed increased NMDAR activation in aging and decreased activation in interictal epilepsy and antibody-positive Anti-NMDAR encephalitis

Role Of Astrocytes On Neuronal Health In Models Of Alzheimer’s Disease

Alzheimer’s disease (AD), one of the major forms of dementia in elderly population, is characterized by amyloid beta (Aβ) plaque along with commonly procured tau hyperphosphorylation. Here, we set to recognize the molecules which are secreted by Aβ1-42 treated astrocytes at very early stage and their probable role in conferring neuroprotection along with improvement in cognitive behavior and pathogenesis of AD. Astrocyte activation has been marked by various specific marker proteins like GFAP, Vimentin, S100β. The conditioned medium obtained from the astrocytes cultured from neonatal pups has been used to check the differential expression of various cytokines in Aβ42 treated astrocytes as compared to control cells. From there soluble intercellular adhesion molecule-1 (sICAM-1) has been noted as a potential candidate. We observed that sICAM-1 protects the cortical neurons from death influenced by Aβ42 oligomers. It attenuates the PARP cleavage caused by Aβ42 and increases the amount of anti-apoptotic proteins such as Bcl-2 and Bcl-xL, along with decrease in the amount of pro-apoptotic protein Bim. TUNEL assay performed both in cortex and hippocampus of Aβ42 infused rat brain and 5xFAD mice brain showed that rrICAM-1 treatment reduced the number of TUNEL positive cells in vivo. Several behavioral experiments namely open field test, contextual and cue dependent fear conditioning, passive avoidance tests, novel object recognition and elevated plus maze that can be related to multiple kinds of memory and learning have displayed that rat recombinant ICAM-1 on being injected within the system intraperitoneally, restored the malfunctioning in the rat behavior caused due to bilateral Aβ42 infusion. We took further interest in checking the underlying disease modifying mechanism rendered by ICAM-1 both in vitro and in vivo systems which might be considered being a therapeutic target for neuroprotection. Mechanistically we observed that ICAM-1 administration decreases NF-κB protein level in AD pathology suggesting that ICAM-1 might play a crucial role in manipulating the stability of NF-κB through multiple degradation process. Also PDTC mediated inhibition of NF-κB protein in 5xFAD transgenic mice brain showed an improvement in cognitive behaviors including learning and memory in mice. Therapeutic approach towards prevalent neurodegenerative diseases like AD is one of the major concerns in the scientific world. Our work suggests that ICAM-1 protein could be said as a potential therapeutic agent that promotes neuronal protection along with recovery in cognitive functioning complemented with clearance of Aβ in Aβ42 infused rats and 5xFAD mice model of AD

Dissecting out the contribution of cognitive, social, and physical activities to environmental enrichment\u27s ability to protect Alzheimer\u27s mice against cognitive impairment

Retrospective studies suggest that lifestyle activities may provide protection against Alzheimer s Disease (AD). However, such studies can be inaccurate and prospective longitudinal studies investigating lifestyle protection against AD are both impractical and impossible to control for. Transgenic (Tg+) AD mice offer a model in a well controlled environment for testing the potential for environmental factors to impact AD development. In an initial study, Tg+ and non-transgenic (Tg-) mice were housed in either environmentally enriched (EE) or standard housing (SH) from 2-6 months of age, with a behavioral battery given during the last 5 weeks of housing. In the Morris maze, platform recognition, and radial arm water maze tasks, Tg+/EE mice were completely protected from cognitive impairment present in Tg+/SH mice and comparable to control Tg-/SH mice in cognitive performance. The current study utilized the same cognitive-based behavioral battery and multimetric statis statistical analysis to investigate the protective effects of complete environment enrichment (EE) versus several of its components (physical activity, social interactions) in AD transgenic mice. The AD transgenic mice utilized develop beta-amyloid (AB) deposition and cognitive impairment by 6-7 months of age. Similar to our initial study, results show that complete EE (physical, social, and cognitive activities) from 2 to 8 months of age completely protected AD transgenic mice from cognitive impairment in tasks representing different cognitive domains - working memory, reference learning, and search/recognition. In strong contrast, Tg+ mice reared in environments that included physical activity and social interaction, or only social interaction, were not protected from cognitive impairment in adulthood -- enhanced cognitive activity was required over and above that present in these other environments. Through use of discriminant function analysis, EE and/or NT mice were consistently discriminated from the poorer performing other housing groups. The cognitive benefits observed in EE-housed Tg+ mice occurred without significant changes in cortical AB levels, plasma cytokine levels, or plasma corticosterone levels, suggesting involvement of mechanisms independent of these endpoints. However, EE-housed Tg+ mice did have decreased dendritic length of neurons in the parietal cortex (but not hippocampus). Noteworthy is that plasma cytokine levels and hippocampal dendritic length consistently correlated with cognitive measures, suggesting their involvement in underlying mechanisms of cognitive performance. The present work provides the first evidence that complete EE (including enhanced cognitive activity) is needed to provide cognitive protection against AD in a Tg+ model of the disease, while the physical and social activity components of EE do not alone lead to protection. These results suggest that humans desiring to gain maximal environmental protection against AD should live a lifestyle high in cognitive, social, and physical activities together

Neuropharmacology and toxicology of novel amphetamine-type stimulants

In recent years there has been a large increase in the use of a new kind of amphetamine- type stimulants known as substituted cathinones. These compounds have a short history of human use, and little is known about their potential neurotoxicity. Two of the most popular substituted cathinones, 4-methylmethcathinone (4-MMC, mephedrone) and 3,4- methylenedioxymethcathinone (MDMC, methylone} are, aside from their β-ketone group, close structural analogues of potentially neurotoxic amphetamines such as methamphetamine (METH) and 3,4-methylenedioxymethamphetamine (MDMA, ecstasy). This has led to concern about the potential neurotoxicity of these novel compounds, and warrants a closer investigation into their possible long-term neurotoxic effects. METHODS The long-term effects of METH and MDMA as well as 4-MMC and MDMC were assessed using a range of biochemical assays, including assessment of monoamine levels and their transporters. The effects on brain activity were investigated using manganese-enhanced magnetic resonance imaging. Furthermore, behavioral experiments assessing cognition and neuropsychiatric function were performed. Finally, in vitro experiments in a neuroblastoma cell line were performed to identify mechanisms responsible for the observed differences in toxicity between the amphetamines and cathinones. RESULTS Unlike METH and MDMA, which produced strong reductions in dopamine and serotonin levels or brain activation, 4-MMC produced few notable effects on monoamine levels and had only minor effects on brain activation, although MDMC produced a reduction in 5-HT levels similar to MDMA. No clear effects on behavioral tests of memory function were observed as both increases and decreases in test performance were seen following 4- MMC and MDMC. In vitro experiments revealed that cathinones differ from amphetamines in their redox properties, and 4-MMC produced different effects than METH on the mitochondrial electron transport chain. CONCLUSIONS The substituted cathinones 4-MMC and MDMC do not appear to be more neurotoxic than METH and MDMA. If anything, they show a more favorable safety profile. Therefore, these substances do not appear to present an imminent and severe threat to public health. From a harm reduction perspective, these compounds may be good alternatives toMETH and MDMA. However, future work is needed to assess with certainty the long- term effects of amphetamine-type stimulants in humans.Miten myrkyllisiä muuntohuumeet ovat? Viime vuosina on tullut saataville uusia huumaavasti vaikuttavia aineita, jotka on hieman muutettu aikaisemmin tunnetuista laittomista huumeista. Näitä muuntohuumeita olivat mm. mefedroni, metyloni, MDPV ja alfa-PVP. Niitä myytiin aluksi internetin kautta, kunnes viranomaiset saivat ne luokitelluksi huumausaineiksi. Suurena huolena näiden uusien aineiden käytössä oli se, ettei niiden myrkyllisyydestä tai pitkäaikaisista haitoista ollut tutkimustuloksia. Käyttäjät ottivatkin suuren riskin kokeillessaan näitä laillisia huumeita (legal highs) heti niiden tullessa saataville. Koska em. aineiden rakenteet muistuttavat metamfetamiinin ja ekstaasin rakenteita, niillä otaksuttiin olevan samanlaisia toksisia vaikutuksia aivoihin ja elimistöön. Tässä työssä tutkittiin kokeellisesti mefedronin ja metylonin mahdollisia haittavaikutuksia aivojen välittäjäaineiden vaikutuksiin ja aivojen aktivaatioon, joiden tiedetään olevan herkkiä huumeiden runsaalle käytölle. Metylonin vaikutukset olivat aivojen hippokampuksessa ja otsalohkossa samankaltaisia kuin ekstaasin, jota se rakenteellisesti muistuttaa. Mefedronilla oli vain vähän pitkäaikaisvaikutuksia verrattuna rakenteellisesti läheiseen tunnetusti myrkylliseen metamfetamiiniin. Mm. sen vaikutus aivojen pitkäaikaiseen aktivaatioon oli erilainen kuin metamfetamiinin, joka vähensi useiden aivoalueiden aktivaatiotilaa vielä kaksi viikkoa 4-päivän annostelun jälkeen. Tulostemme perusteella näyttävät pienet erot stimulanttihuumeiden rakenteissa vaikuttavan käytön aiheuttamiin pitkäaikaishaittoihin, vaikka aineet edelleen omaavat riippuvuutta ylläpitävän päihdevaikutuksensa. Jatkotutkimuksia näistä aineista tarvitaan, ja jatkossakin saataville tulevien uusien muuntohuumeiden haittoja tulisi pystyä aktiivisesti selvittämään. Terveyspolitiikan ja haittojen minimointiin pyrkivän päihdepolitiikan tulisi tähdätä sekä käytön minimointiin ja sen suuntaamiseen mahdollisimman vähän haitallisiin päihteisiin