We examined white matter abnormalities in patients with a distinctive extrapyramidal syndrome due to intravenous methcathinone (ephedrone) abuse. We performed diffusion tensor imaging in ten patients and fifteen age-matched controls to assess white matter structure across the whole brain. Diffuse significant decreases in white matter fractional anisotropy, a diffusion tensor imaging metric which reflects microstructural integrity, occurred in the patients compared with controls. In addition, we identified two foci of severe white matter abnormality underlying the right ventral premotor cortex and the medial frontal cortex, two cortical regions involved in higher-level executive control of motor function. Paths connecting different cortical regions with the globus pallidus, the nucleus previously shown to be abnormal on structural imaging in these patients, were generated using probabilistic tractography. The fractional anisotropy within all these tracts was lower in the patient group than controls. Finally, we tested for a relationship between white matter integrity and clinical outcome. We identified a region within the left corticospinal tract in which lower fractional anisotropy was associated with greater functional deficit but this region did not show reduced fractional anisotropy in the overall patient group compared to controls. These patients have widespread white matter damage with greatest severity of damage underlying executive motor areas.
Extrapyramidal syndrome; Methcathinone; Manganese toxicity; diffusion imaging; white matter tracts
Scar tissue at sites of traumatic injury in the adult central nervous system presents a combined physical and molecular impediment to axon regeneration. Of multiple known central nervous system scar associated axon growth inhibitors, semaphorin 3A has been shown to be strongly expressed by invading leptomeningeal fibroblasts. We have previously demonstrated that infusion of the small leucine-rich proteoglycan decorin results in major suppression of several growth inhibitory chondroitin sulphate proteoglycans and growth of adult sensory axons across acute spinal cord injuries. Furthermore, decorin treatment of leptomeningeal fibroblasts significantly increases their ability to support neurite growth of co-cultured adult dorsal root ganglion neurons. In the present study we show that decorin has the ability to suppress semaphorin 3A expression within adult rat cerebral cortex scar tissue and in primary leptomeningeal fibroblasts in vitro. Infusion of decorin core protein for eight days resulted in a significant reduction of semaphorin 3A messenger RNA expression within injury sites compared with saline-treated control animals. Both in situ hybridization and immunostaining confirmed that semaphorin 3A messenger RNA expression and protein levels are significantly reduced in decorin-treated animals. Similarly, decorin treatment decreased the expression of semaphorin 3A messenger RNA in cultured rat leptomeningeal fibroblasts compared with untreated cells. Mechanistic studies revealed that decorin-mediated suppression of semaphorin 3A critically depends on erythroblastic leukaemia viral oncogene homologue B4 and signal transducer and activator of transcription 3 function. Collectively, our studies show that in addition to suppressing the levels of inhibitory chondroitin sulphate proteoglycans, decorin has the ability to suppress semaphorin 3A in the injured central nervous system. Our findings provide further evidence for the use of decorin as a potential therapy for promoting axonal growth and repair in the injured adult mammalian brain and spinal cord.
decorin; scar; semaphorin; ErbB4; STAT3
Hippocampal atrophy, posterior cingulate and frontal glucose hypometabolism, and white-matter tract disruption are well-described early macroscopic events in Alzheimer’s disease. The relationships between these three types of alterations have been documented in previous studies, but their chronology still remains to be established. The present study used multi-modal Fluorodeoxyglucose - Positron Emission Tomography and Magnetic Resonance Imaging longitudinal data to address this question in patients with amnestic Mild Cognitive Impairment. We found unidirectional, specific sequential relationships between: i) baseline hippocampal atrophy and both cingulum bundle (r=0.70; p=3.10−3) and uncinate fasciculus (r=0.75; p=7.10−4) rate of atrophy; ii) baseline cingulum bundle atrophy and rate of decline of posterior (r=0.72; p=2.10−3) and anterior (r=0.74; p=1.10−3) cingulate metabolism; and iii) baseline uncinate white matter atrophy and subgenual metabolism rate of change (r=0.65; p=6.10−3). Baseline local grey matter atrophy was not found to contribute to hypometabolism progression within the posterior and anterior cingulate as well as subgenual cortices. These findings suggest that hippocampal atrophy progressively leads to disruption of the cingulum bundle and uncinate fasciculus, which in turn leads to glucose hypometabolism of the cingulate and subgenual cortices, respectively. This study reinforces the relevance of remote mechanisms above local interactions to account for the patterns of brain alteration observed in amnestic Mild Cognitive Impairment, and provides new avenues to assess the sequence of events in complex diseases characterized by multiple manifestations.
Aged; Aged, 80 and over; Alzheimer Disease; metabolism; pathology; Atrophy; Brain; metabolism; pathology; Cerebral Cortex; metabolism; pathology; Female; Follow-Up Studies; Hippocampus; metabolism; pathology; Humans; Magnetic Resonance Imaging; Male; Middle Aged; Nerve Fibers, Myelinated; metabolism; pathology; Time Factors; Alzheimers disease; MRI/fMRI; PET imaging; white matter; hippocampus
Our aim was to examine how brain imaging in the initial phase of a stroke could predict both acute/subacute as well as chronic spatial neglect. We present the first voxel-wise longitudinal lesion-behaviour mapping study, examining acute/subacute as well as chronic performance in the same individuals. Acute brain imaging (acquired on average 6.2 days post-injury) was used to evaluate neglect symptoms at the initial (mean 12.4 days post-stroke) and the chronic (mean 491 days) phase of the stroke. Chronic neglect was found in about one-third of the patients with acute neglect. Analysis suggests that lesion of the superior and middle temporal gyri predict both acute/subacute as well as chronic neglect. At the subcortical level, the basal ganglia as well as the inferior occipitofrontal fasciculus/extreme capsule appear to play a significant role for both acute/subacute as well as chronic neglect. Beyond, the uncinate fasciculus was critically related to the emergence of chronic spatial neglect. We infer that individuals who experience spatial neglect in the initial phase of the stroke yet do not have injury to these cortical and subcortical structures are likely to recover, and thus have a favourable prognosis.
spatial neglect; anatomy; prognosis; chronic; acute; recovery; plasticity; stroke; human
Motor axon degeneration is a critical but poorly understood event leading to weakness and muscle atrophy in motor neuron diseases. Here, we investigated oxidative stress-mediated axonal degeneration in mice lacking the antioxidant enzyme, Cu,Zn superoxide dismutase (SOD1). We demonstrate a progressive motor axonopathy in these mice and show that Sod1−/− primary motor neurons extend short axons in vitro with reduced mitochondrial density. Sod1−/− neurons also show oxidation of mitochondrial—but not cytosolic—thioredoxin, suggesting that loss of SOD1 causes preferential oxidative stress in mitochondria, a primary source of superoxide in cells. SOD1 is widely regarded as the cytosolic isoform of superoxide dismutase, but is also found in the mitochondrial intermembrane space. The functional significance of SOD1 in the intermembrane space is unknown. We used a transgenic approach to express SOD1 exclusively in the intermembrane space and found that mitochondrial SOD1 is sufficient to prevent biochemical and morphological defects in the Sod1−/− model, and to rescue the motor phenotype of these mice when followed to 12 months of age. These results suggest that SOD1 in the mitochondrial intermembrane space is fundamental for motor axon maintenance, and implicate oxidative damage initiated at mitochondrial sites in the pathogenesis of motor axon degeneration.
SOD; axon; neuromuscular junction; motor neuron disease; mitochondria
Autophagy, a major degradative pathway for proteins and organelles, is essential for survival of mature neurons. Extensive autophagic-lysosomal pathology in Alzheimer’s disease brain contributes to Alzheimer’s disease pathogenesis, although the underlying mechanisms are not well understood. Here, we identified and characterized marked intraneuronal amyloid-β peptide/amyloid and lysosomal system pathology in the Alzheimer’s disease mouse model TgCRND8 similar to that previously described in Alzheimer’s disease brains. We further establish that the basis for these pathologies involves defective proteolytic clearance of neuronal autophagic substrates including amyloid-β peptide. To establish the pathogenic significance of these abnormalities, we enhanced lysosomal cathepsin activities and rates of autophagic protein turnover in TgCRND8 mice by genetically deleting cystatin B, an endogenous inhibitor of lysosomal cysteine proteases. Cystatin B deletion rescued autophagic-lysosomal pathology, reduced abnormal accumulations of amyloid-β peptide, ubiquitinated proteins and other autophagic substrates within autolysosomes/lysosomes and reduced intraneuronal amyloid-β peptide. The amelioration of lysosomal function in TgCRND8 markedly decreased extracellular amyloid deposition and total brain amyloid-β peptide 40 and 42 levels, and prevented the development of deficits of learning and memory in fear conditioning and olfactory habituation tests. Our findings support the pathogenic significance of autophagic-lysosomal dysfunction in Alzheimer’s disease and indicate the potential value of restoring normal autophagy as an innovative therapeutic strategy for Alzheimer’s disease.
autophagy; lysosome; cystatin B; cathepsin; Alzheimer’s disease
Leber’s hereditary optic neuropathy, the most frequent mitochondrial disease due to mitochondrial DNA point mutations in complex I, is characterized by the selective degeneration of retinal ganglion cells, leading to optic atrophy and loss of central vision prevalently in young males. The current study investigated the reasons for the higher prevalence of Leber’s hereditary optic neuropathy in males, exploring the potential compensatory effects of oestrogens on mutant cell metabolism. Control and Leber’s hereditary optic neuropathy osteosarcoma-derived cybrids (11778/ND4, 3460/ND1 and 14484/ND6) were grown in glucose or glucose-free, galactose-supplemented medium. After having shown the nuclear and mitochondrial localization of oestrogen receptors in cybrids, experiments were carried out by adding 100 nM of 17β-oestradiol. In a set of experiments, cells were pre-incubated with the oestrogen receptor antagonist ICI 182780. Leber’s hereditary optic neuropathy cybrids in galactose medium presented overproduction of reactive oxygen species, which led to decrease in mitochondrial membrane potential, increased apoptotic rate, loss of cell viability and hyper-fragmented mitochondrial morphology compared with control cybrids. Treatment with 17β-oestradiol significantly rescued these pathological features and led to the activation of the antioxidant enzyme superoxide dismutase 2. In addition, 17β-oestradiol induced a general activation of mitochondrial biogenesis and a small although significant improvement in energetic competence. All these effects were oestrogen receptor mediated. Finally, we showed that the oestrogen receptor β localizes to the mitochondrial network of human retinal ganglion cells. Our results strongly support a metabolic basis for the unexplained male prevalence in Leber’s hereditary optic neuropathy and hold promises for a therapeutic use for oestrogen-like molecules.
LHON; oestrogen; mitochondrial disorders; oestrogen receptors; oxidative stress
Huntington’s disease is an autosomal dominant brain disease. Although conceptualized as a neurodegenerative disease of the striatum, a growing number of studies challenge this classic concept of Huntington’s disease aetiology. Intracranial volume is the tissue and fluid within the calvarium and is a representation of the maximal brain growth obtained during development. The current study reports intracranial volume obtained from an magnetic resonance imaging brain scan in a sample of subjects (n = 707) who have undergone presymptomatic gene testing. Participants who are gene-expanded but not yet manifesting the disease (prodromal Huntington’s disease) are compared with subjects who are non-gene expanded. The prodromal males had significantly smaller intracranial volume measures with a mean volume that was 4% lower compared with controls. Although the prodromal females had smaller intracranial volume measures compared with their controls, this was not significant. The current findings suggest that mutant huntingtin can cause abnormal development, which may contribute to the pathogenesis of Huntington’s disease.
brain; brain imaging; brain volumes
A compelling single case report of visual awareness (visual qualia) without primary visual cortex would be sufficient to refute the hypothesis that the primary visual cortex and the back-projections to it are necessary for conscious visual experience. In a previous study, we emphasized the presence of crude visual awareness in Patient G.Y., with a lesion of the primary visual cortex, who is aware of, and able to discriminate, fast-moving visual stimuli presented to his blind field. The visual nature of Patient G.Y.’s blind field experience has since been questioned and it has been suggested that the special circumstances of repeated testing over decades may have altered Patient G.Y.’s visual pathways. We therefore sought new evidence of visual awareness without primary visual cortex in patients for whom such considerations do not apply. Three patients with hemianopic field defects (Patient G.N. and Patient F.B. with MRI confirmed primary visual cortex lesions, Patient C.G. with an inferred lesion) underwent detailed psychophysical testing in their blind fields. Visual stimuli were presented at different velocities and contrasts in two- and four-direction discrimination experiments and the direction of motion and awareness reported using a forced-choice paradigm. Detailed verbal reports were also obtained of the nature of the blind field experience with comparison of the drawings of the stimulus presented in the blind and intact fields, where possible. All three patients reported visual awareness in their blind fields. Visual awareness was significantly more likely when a moving stimulus was present compared to no stimulus catch trials (P < 0.01 for each subject). Psychophysical performance in Patient F.B. and Patient G.N. was consistent with the Riddoch syndrome, with higher levels of visual awareness for moving compared to static stimuli (P < 0.001) and intact direction discrimination (P < 0.0001 for two- and four-direction experiments). Although the blind field experience of all three subjects was degraded, it was clearly visual in nature. We conclude that the primary visual cortex or back-projections to it are not necessary for visual awareness.
visual consciousness; blindsight; feedback; V1; Riddoch syndrome
Past studies show beneficial as well as detrimental effects of subthalamic nucleus deep-brain stimulation on impulsive behaviour. We address this paradox by investigating individuals with Parkinson’s disease treated with subthalamic nucleus stimulation (n = 17) and healthy controls without Parkinson’s disease (n = 17) on performance in a Simon task. In this reaction time task, conflict between premature response impulses and goal-directed action selection is manipulated. We applied distributional analytic methods to separate the strength of the initial response impulse from the proficiency of inhibitory control engaged subsequently to suppress the impulse. Patients with Parkinson’s disease were tested when stimulation was either turned on or off. Mean conflict interference effects did not differ between controls and patients, or within patients when stimulation was on versus off. In contrast, distributional analyses revealed two dissociable effects of subthalamic nucleus stimulation. Fast response errors indicated that stimulation increased impulsive, premature responding in high conflict situations. Later in the reaction process, however, stimulation improved the proficiency with which inhibitory control was engaged to suppress these impulses selectively, thereby facilitating selection of the correct action. This temporal dissociation supports a conceptual framework for resolving past paradoxical findings and further highlights that dynamic aspects of impulse and inhibitory control underlying goal-directed behaviour rely in part on neural circuitry inclusive of the subthalamic nucleus.
Parkinson’s disease; deep-brain stimulation; response inhibition; impulsivity; subthalamic nucleus
The basal ganglia are thought to be important in the selection of wanted and the suppression of unwanted motor patterns according to explicit rules (i.e. response inhibition). The subthalamic nucleus has been hypothesized to play a particularly critical role in this function. Deep brain stimulation of the subthalamic nucleus in individuals with Parkinson’s disease has been used to test this hypothesis, but results have been variable. Based on current knowledge of the anatomical organization of the subthalamic nucleus, we propose that the location of the contacts used in deep brain stimulation could explain variability in the effects of deep brain stimulation of the subthalamic nucleus on response inhibition tasks. We hypothesized that stimulation affecting the dorsal subthalamic nucleus (connected to the motor cortex) would be more likely to affect motor symptoms of Parkinson’s disease, and stimulation affecting the ventral subthalamic nucleus (connected to higher order cortical regions) would be more likely to affect performance on a response inhibition task. We recruited 10 individuals with Parkinson’s disease and bilateral deep brain stimulation of the subthalamic nucleus with one contact in the dorsal and another in the ventral subthalamic region on one side of the brain. Patients were tested with a Go–No-Go task and a motor rating scale in three conditions: stimulation off, unilateral dorsal stimulation and unilateral ventral stimulation. Both dorsal and ventral stimulation improved motor symptoms, but only ventral subthalamic stimulation affected Go–No-Go performance, decreasing hits and increasing false alarms, but not altering reaction times. These results suggest that the ventral subthalamic nucleus is involved in the balance between appropriate selection and inhibition of prepotent responses in cognitive paradigms, but that a wide area of the subthalamic nucleus region is involved in the motor symptoms of Parkinson’s disease. This finding has implications for resolving inconsistencies in previous research, highlights the role of the ventral subthalamic nucleus region in response inhibition and suggests an approach for the clinical optimization of deep brain stimulation of the subthalamic nucleus for both motor and cognitive functions.
subthalamic nucleus; deep brain stimulation; response inhibition; Parkinson’s disease
Studies of head size and brain volume in autism spectrum disorders have suggested that early cortical overgrowth may be followed by prematurely arrested growth. However, the few investigations quantifying cortical thickness have yielded inconsistent results, probably due to variable ages and/or small sample sizes. We assessed differences in cortical thickness between high-functioning adolescent and young adult males with autism spectrum disorders (n = 41) and matched typically developing males (n = 40). We hypothesized thinner cortex, particularly in frontal, parietal and temporal regions, for individuals with autism spectrum disorders in comparison with typically developing controls. Furthermore, we expected to find an age × diagnosis interaction: with increasing age, more pronounced cortical thinning would be observed in autism spectrum disorders than typically developing participants. T1-weighted magnetization prepared rapid gradient echo 3 T magnetic resonance imaging scans were acquired from high-functioning males with autism spectrum disorders and from typically developing males matched group-wise on age (range 12–24 years), intelligence quotient (≥85) and handedness. Both gyral-level and vertex-based analyses revealed significantly thinner cortex in the autism spectrum disorders group that was located predominantly in left temporal and parietal regions (i.e. the superior temporal sulcus, inferior temporal, postcentral/superior parietal and supramarginal gyri). These findings remained largely unchanged after controlling for intelligence quotient and after accounting for psychotropic medication usage and comorbid psychopathology. Furthermore, a significant age × diagnosis interaction was found in the left fusiform/inferior temporal cortex: participants with autism spectrum disorders had thinner cortex in this region with increasing age to a greater degree than did typically developing participants. Follow-up within group comparisons revealed significant age-related thinning in the autism spectrum disorders group but not in the typically developing group. Both thinner temporal and parietal cortices during adolescence and young adulthood and discrepantly accelerated age-related cortical thinning in autism spectrum disorders suggest that a second period of abnormal cortical growth (i.e. greater thinning) may be characteristic of these disorders.
autism; brain; MRI; cortical thickness; age-related changes
Impaired consciousness requires altered cortical function. This can occur either directly from disorders that impair widespread bilateral regions of the cortex or indirectly through effects on subcortical arousal systems. It has therefore long been puzzling why focal temporal lobe seizures so often impair consciousness. Early work suggested that altered consciousness may occur with bilateral or dominant temporal lobe seizure involvement. However, other bilateral temporal lobe disorders do not impair consciousness. More recent work supports a ‘network inhibition hypothesis’ in which temporal lobe seizures disrupt brainstem–diencephalic arousal systems, leading indirectly to depressed cortical function and impaired consciousness. Indeed, prior studies show subcortical involvement in temporal lobe seizures and bilateral frontoparietal slow wave activity on intracranial electroencephalography. However, the relationships between frontoparietal slow waves and impaired consciousness and between cortical slowing and fast seizure activity have not been directly investigated. We analysed intracranial electroencephalography recordings during 63 partial seizures in 26 patients with surgically confirmed mesial temporal lobe epilepsy. Behavioural responsiveness was determined based on blinded review of video during seizures and classified as impaired (complex-partial seizures) or unimpaired (simple-partial seizures). We observed significantly increased delta-range 1–2 Hz slow wave activity in the bilateral frontal and parietal neocortices during complex-partial compared with simple-partial seizures. In addition, we confirmed prior work suggesting that propagation of unilateral mesial temporal fast seizure activity to the bilateral temporal lobes was significantly greater in complex-partial than in simple-partial seizures. Interestingly, we found that the signal power of frontoparietal slow wave activity was significantly correlated with the temporal lobe fast seizure activity in each hemisphere. Finally, we observed that complex-partial seizures were somewhat more common with onset in the language-dominant temporal lobe. These findings provide direct evidence for cortical dysfunction in the form of bilateral frontoparietal slow waves associated with impaired consciousness in temporal lobe seizures. We hypothesize that bilateral temporal lobe seizures may exert a powerful inhibitory effect on subcortical arousal systems. Further investigations will be needed to fully determine the role of cortical-subcortical networks in ictal neocortical dysfunction and may reveal treatments to prevent this important negative consequence of temporal lobe epilepsy.
cortex; EEG; seizures; temporal lobe epilepsy; consciousness
Episodic ataxia type 1 is a neuronal channelopathy caused by mutations in the KCNA1 gene encoding the fast K+ channel subunit Kv1.1. Episodic ataxia type 1 presents with brief episodes of cerebellar dysfunction and persistent neuromyotonia and is associated with an increased incidence of epilepsy. In myelinated peripheral nerve, Kv1.1 is highly expressed in the juxtaparanodal axon, where potassium channels limit the depolarizing afterpotential and the effects of depolarizing currents. Axonal excitability studies were performed on patients with genetically confirmed episodic ataxia type 1 to characterize the effects of Kv1.1 dysfunction on motor axons in vivo. The median nerve was stimulated at the wrist and compound muscle action potentials were recorded from abductor pollicis brevis. Threshold tracking techniques were used to record strength-duration time constant, threshold electrotonus, current/threshold relationship and the recovery cycle. Recordings from 20 patients from eight kindreds with different KCNA1 point mutations were compared with those from 30 normal controls. All 20 patients had a history of episodic ataxia and 19 had neuromyotonia. All patients had similar, distinctive abnormalities: superexcitability was on average 100% higher in the patients than in controls (P < 0.00001) and, in threshold electrotonus, the increase in excitability due to a depolarizing current (20% of threshold) was 31% higher (P < 0.00001). Using these two parameters, the patients with episodic ataxia type 1 and controls could be clearly separated into two non-overlapping groups. Differences between the different KCNA1 mutations were not statistically significant. Studies of nerve excitability can identify Kv1.1 dysfunction in patients with episodic ataxia type 1. The simple 15 min test may be useful in diagnosis, since it can differentiate patients with episodic ataxia type 1 from normal controls with high sensitivity and specificity.
ataxia; channelopathy; nerve excitability; neuromyotonia; potassium channel
Screening tests for Alzheimer’s disease lack sensitivity and specificity. We developed the AD8, a brief dementia screening interview validated against clinical and cognitive evaluations, as an improvement over current screening methods. Because insufficient follow-up has occurred to validate the AD8 against the neuropathologic findings of Alzheimer’s disease, we investigated whether AD8 scores correspond to impairment in episodic memory testing and changes in biomarkers of Alzheimer’s disease (cerebrospinal fluid and amyloid imaging with Pittsburgh compound B) characteristic of symptomatic Alzheimer’s disease. We also compared informant-based assessments with brief performance-based dementia screening measurements such as the Mini Mental State Exam. The sample (n = 257) had a mean age of 75.4 years with 15.1 years of education; 88.7% were Caucasian and 45.5% were male. The sample was divided into two groups based on their AD8 scores: those with a negative dementia screening test (AD8 score 0 or 1, n = 137) and those with a positive dementia screening test (AD8 score ≥2, n = 120). Individuals with positive AD8 scores had abnormal Pittsburgh compound B binding (P < 0.001) and cerebrospinal fluid biomarkers (P < 0.001) compared with individuals with negative AD8 scores. Individuals with positive AD8 tests and positive biomarkers scored in the impaired range on the Wechsler Logical Memory Story A (mean score 7.0 ± 4.5 for Pittsburgh compound B; mean score 7.6 ± 5.3 for cerebrospinal fluid amyloid beta protein 1–42). The AD8 area under the curve for Pittsburgh compound B was 0.737 (95% confidence interval: 0.64–0.83) and for cerebrospinal fluid amyloid beta protein 1–42 was 0.685 (95% confidence interval: 0.60–0.77) suggesting good discrimination. The AD8 had superior sensitivity in detecting early stages of dementia compared with the Mini Mental State Examination. The AD8 had a likelihood ratio of a positive test of 5.8 (95% confidence interval: 5.4–6.3) and likelihood ratio of a negative test of 0.04 (95% confidence interval: 0.03–0.06), increasing the pre-test probability of an individual having symptomatic Alzheimer’s disease. Individuals with AD8 scores of ≥2 had a biomarker phenotype consistent with Alzheimer’s disease and lower performance on episodic memory tests, supporting a diagnosis of Alzheimer’s disease. Informant-based assessments may be superior to performance-based screening measures such as the Mini Mental State Examination in corresponding to underlying Alzheimer’s disease pathology, particularly at the earliest stages of decline. The use of a brief test such as the AD8 may improve strategies for detecting dementia in community settings where biomarkers may not be readily available, and may enrich clinical trial recruitment by increasing the likelihood that participants have underlying biomarker abnormalities.
AD8; Alzheimer’s disease; screening; biomarkers; preclinical; cognition
Short echo time localized proton magnetic resonance spectroscopy provides quantification of brain metabolites, including N-acetyl-aspartate, myo-inositol, creatine/phosphocreatine and choline-containing compounds, which may be useful biomarkers for monitoring Alzheimer's disease. We aimed to quantify the rate of metabolite change in Alzheimer's disease, to assess factors influencing changes and to investigate the potential for serial magnetic resonance spectroscopy as an Alzheimer's disease trial biomarker. A total of 42 patients and 22 controls each had up to six magnetic resonance spectroscopy examinations over a 2-year period, using a midline posterior cingulate single-voxel point resolved spectroscopy sequence (1.5 T; time to repetition = 2000 ms; echo time = 30 ms; 192 averages). Metabolite ratios N-acetyl-aspartate:creatine/phosphocreatine, choline-containing compounds:creatine/phosphocreatine, and myo-inositol:creatine/phosphocreatine were measured using online software (PROBE-Q) and the N-acetyl-aspartate:myo-inositol ratio was derived. Baseline ratios were compared between patients and controls. A linear mixed model was used to quantify longitudinal changes and extended to assess the effect of age, disease severity and baseline use of acetylcholinesterase inhibitors. Patients and controls were matched for age (patients: 68.9 ± 7.2 years; controls: 69.1 ± 6.7 years); 71% of the patients were on acetylcholinesterase inhibitors at baseline; mean Mini-Mental State Examination for patients was 19.4 ± 4.1. A total of 307 spectra were acquired. In cross-sectional analyses, patients were significantly different from controls for N-acetyl-aspartate:creatine/phosphocreatine (11% lower, P < 0.001), N-acetyl-aspartate:myo-inositol (24% lower, P < 0.001), and myo-inositol:creatine/phosphocreatine (17% higher, P < 0.001). After adjustment for N-acetyl-aspartate:myo-inositol, none of the other variables differed significantly. In patients there was significant decline in N-acetyl-aspartate:creatine/phosphocreatine (mean: 2.2%/year; 95% confidence interval: 0.9–3.5) and N-acetyl-aspartate:myo-inositol (mean: 3.7%/year; 95% confidence interval: 1.7–5.7), with no evidence for influence by age, disease severity or acetylcholinesterase inhibitor use. There was significant excess decline in patients compared with controls only in N-acetyl-aspartate:myo-inositol (mean: 3.6%/year; 95% confidence interval: 0.8–6.4; P = 0.014). Between-subject standard deviation for N-acetyl-aspartate:myo-inositol was 0% for controls and 3.5%/year for patients; within-subject standard deviation for a 1 year, two-time-point study was 9.2%/year for both patients and controls. These results confirm that magnetic resonance spectroscopy can be used to quantify excess metabolite decline in Alzheimer's disease, which may provide a useful measure of disease progression. We found no evidence that age, disease severity or acetylcholinesterase inhibitor use influenced rate of decline, although numbers were small. The substantial variability in longitudinal measurements that drives sample size requirements is principally within-subject and technique related: technical developments to reduce this variability may make serial magnetic resonance spectroscopy a viable biomarker in clinical trials for Alzheimer's disease.
Alzheimer's disease; magnetic resonance spectroscopy; clinical trial design