Nadia Postupna

Diet Intervention and Cerebrospinal Fluid Biomarkers in Amnestic Mild Cognitive Impairment

OBJECTIVE To compare the effects of a 4-week high-saturated fat/high-glycemic index (HIGH) diet with a low-saturated fat/low-glycemic index (LOW) diet on insulin and lipid metabolism, cerebrospinal fluid (CSF) markers of Alzheimer disease, and cognition for healthy adults and adults with amnestic mild cognitive impairment (aMCI). DESIGN Randomized controlled trial. SETTING Veterans Affairs Medical Center clinical research unit. PARTICIPANTS Forty-nine older adults (20 healthy adults with a mean [SD] age of 69.3 [7.4] years and 29 adults with aMCI with a mean [SD] age of 67.6 [6.8] years). INTERVENTION Participants received the HIGH diet (fat, 45% [saturated fat, > 25%]; carbohydrates, 35%-40% [glycemic index, > 70]; and protein, 15%-20%) or the LOW diet (fat, 25%; [saturated fat, < 7%]; carbohydrates, 55%-60% [glycemic index, < 55]; and protein, 15%-20%) for 4 weeks. Cognitive tests, an oral glucose tolerance test, and lumbar puncture were conducted at baseline and during the fourth week of the diet. MAIN OUTCOME MEASURES The CSF concentrations of β-amyloid (Aβ42 and Aβ40), tau protein, insulin, F2-isoprostanes, and apolipoprotein E, plasma lipids and insulin, and measures of cognition. RESULTS For the aMCI group, the LOW diet increased CSF Aβ42 concentrations, contrary to the pathologic pattern of lowered CSF Aβ42 typically observed in Alzheimer disease. The LOW diet had the opposite effect for healthy adults, ie, decreasing CSF Aβ42, whereas the HIGH diet increased CSF Aβ42. The CSF apolipoprotein E concentration was increased by the LOW diet and decreased by the HIGH diet for both groups. For the aMCI group, the CSF insulin concentration increased with the LOW diet, but the HIGH diet lowered the CSF insulin concentration for healthy adults. The HIGH diet increased and the LOW diet decreased plasma lipids, insulin, and CSF F2-isoprostane concentrations. Delayed visual memory improved for both groups after completion of 4 weeks of the LOW diet. CONCLUSION Our results suggest that diet may be a powerful environmental factor that modulates Alzheimer disease risk through its effects on central nervous system concentrations of Aβ42, lipoproteins, oxidative stress, and insulin.

High frequency deep brain stimulation: what are the therapeutic mechanisms?

High frequency deep brain stimulation (HFS) used to treat the symptoms of Parkinsons disease (PD) was first assumed to act by reducing an excessive tonic GABAergic inhibitory output from the internal globus pallidus (GPi). Stimulation in GPi might produce this directly by mechanisms such as depolarization block or activation of presynaptic inhibitory fibers, and the same mechanisms evoked by HFS in the subthalamic nucleus (STN) could reduce the excitatory action of STN on GPi neurons. Although somatic recordings from neurons near the stimulation site may appear to support this potential mechanism, the action downstream from the site of stimulation often is not consistent with this interpretation. A more parsimonious explanation for the similar effects of HFS in STN or GPi and a lesion of either of these structures is that both HFS and pallidotomy interrupt an abnormal pattern of firing in cortico-basal ganglia-thalamocortical loops that is responsible for the symptoms of PD.

Effect of apolipoprotein e genotype and diet on apolipoprotein e lipidation and amyloid peptides randomized clinical trial

IMPORTANCE Sporadic Alzheimer disease (AD) is caused in part by decreased clearance of the β-amyloid (Aβ) peptide breakdown products. Lipid-depleted (LD) apolipoproteins are less effective at binding and clearing Aβ, and LD Aβ peptides are more toxic to neurons. However, not much is known about the lipid states of these proteins in human cerebrospinal fluid. OBJECTIVE To characterize the lipidation states of Aβ peptides and apolipoprotein E in the cerebrospinal fluid in adults with respect to cognitive diagnosis and APOE ε4 allele carrier status and after a dietary intervention. DESIGN Randomized clinical trial. SETTING Veterans Affairs Medical Center clinical research unit. PARTICIPANTS Twenty older adults with normal cognition (mean [SD] age, 69 [7] years) and 27 with amnestic mild cognitive impairment (67 [6] years). INTERVENTIONS Randomization to a diet high in saturated fat content and with a high glycemic index (High diet; 45% of energy from fat [>25% saturated fat], 35%-40% from carbohydrates with a mean glycemic index >70, and 15%-20% from protein) or a diet low in saturated fat content and with a low glycemic index (Low diet; 25% of energy from fat [<7% saturated fat], 55%-60% from carbohydrates with a mean glycemic index <55, and 15%-20% from protein). MAIN OUTCOMES AND MEASURES Lipid-depleted Aβ42 and Aβ40 and apolipoprotein E in cerebrospinal fluid. RESULTS Baseline levels of LD Aβ were greater for adults with mild cognitive impairment compared with adults with normal cognition (LD Aβ42, P = .05; LD Aβ40, P = .01). These findings were magnified in adults with mild cognitive impairment and the ε4 allele, who had higher LD apolipoprotein E levels irrespective of cognitive diagnosis (P < .001). The Low diet tended to decrease LD Aβ levels, whereas the High diet increased these fractions (LD Aβ42, P = .01; LD Aβ40, P = .15). Changes in LD Aβ levels with the Low diet negatively correlated with changes in cerebrospinal fluid levels of insulin (LD Aβ42 and insulin, r = -0.68 [P = .01]; LD Aβ40 and insulin, r = -0.78 [P = .002]). CONCLUSIONS AND RELEVANCE The lipidation states of apolipoproteins and Aβ peptides in the brain differ depending on APOE genotype and cognitive diagnosis. Concentrations can be modulated by diet. These findings may provide insight into the mechanisms through which apolipoprotein E4 and unhealthy diets impart risk for developing AD.

Pathologic Correlates of Dementia in Individuals with Lewy Body Disease

Cognitive impairment and dementia are more common in patients with Parkinson disease (PD) than age‐matched controls and appear to become more frequent as PD progresses. However, estimates of dementia in patients with PD have varied widely, likely due in part to differences in case definition, case ascertainment and methodology. First, we review investigations of usual pathologic correlates of dementia in patients with brainstem (b) Lewy Body Disease (LBD) and report our findings from the initial 266 brain autopsies from a population‐based study of brain aging and incident dementia. Our results showed that 2.6% of subjects were diagnosed with PD during life but that 20% had bLBD at autopsy. Seventy percent of individuals with bLBD had high level of one or more cerebral pathologic changes significantly associated with dementia: Alzheimers disease (AD), cerebral (c) LBD or microvascular brain injury (µVBI); these were commonly co‐morbid. Next we consider proposed contributors to cognitive impairment and dementia in the approximately 30% of patients with only bLBD, including regionally selective dendritic degeneration of neostriatal medium spiny neurons. Diseases contributing to cognitive impairment and dementia in patients with bLBD are heterogeneous, providing diagnostic challenges as well as multiple opportunities for successful intervention in patients with PD.

Severely Impaired Learning and Altered Neuronal Morphology in Mice Lacking NMDA Receptors in Medium Spiny Neurons

The striatum is composed predominantly of medium spiny neurons (MSNs) that integrate excitatory, glutamatergic inputs from the cortex and thalamus, and modulatory dopaminergic inputs from the ventral midbrain to influence behavior. Glutamatergic activation of AMPA, NMDA, and metabotropic receptors on MSNs is important for striatal development and function, but the roles of each of these receptor classes remain incompletely understood. Signaling through NMDA-type glutamate receptors (NMDARs) in the striatum has been implicated in various motor and appetitive learning paradigms. In addition, signaling through NMDARs influences neuronal morphology, which could underlie their role in mediating learned behaviors. To study the role of NMDARs on MSNs in learning and in morphological development, we generated mice lacking the essential NR1 subunit, encoded by the Grin1 gene, selectively in MSNs. Although these knockout mice appear normal and display normal 24-hour locomotion, they have severe deficits in motor learning, operant conditioning and active avoidance. In addition, the MSNs from these knockout mice have smaller cell bodies and decreased dendritic length compared to littermate controls. We conclude that NMDAR signaling in MSNs is critical for normal MSN morphology and many forms of learning.

High-intensity physical activity modulates diet effects on cerebrospinal amyloid-β levels in normal aging and mild cognitive impairment.

We previously showed that amyloid-β 1-42 (Aβ(42)) levels in cerebrospinal fluid (CSF) were markedly altered in response to a 4-week dietary intervention in normal aging and mild cognitive impairment (MCI). Here, we re-examined the data to assess whether diet-induced effects on CSF Aβ(42) were modulated by high intensity physical activity (hi-PA). Normal older adults (n = 18, mean age = 68.6 ± 7.4 y) and adults with amnestic MCI (n = 23, mean age = 68.0 ± 6.5 y) received a low saturated fat/low glycemic index (LOW) diet or a high saturated fat/high glycemic index (HIGH) diet, and CSF levels of Aβ(42), tau, and IL-8 were measured at baseline and week 4. Pre-study activity levels were assessed using a 7-d questionnaire, and weekly duration of hi-PA was quantified. At baseline, increased hi-PA in normals predicted lower CSF levels of tau (r = -0.54, p = 0.020) and IL-8 (r = -0.70, p = 0.025). Diet-induced effects on CSF Aβ(42) during the intervention study were modulated by hi-PA, and the nature of this effect differed for normals and MCI (ANOVA, p = 0.039). That is, for normal adults, increased hi-PA attenuated the effects of the HIGH diet on CSF Aβ(42) whereas in MCI, increased hi-PA potentiated the effects of the LOW diet. Our results suggest that normal adults who engage in hi-PA are less vulnerable to the pathological effects of an unhealthy diet, while in MCI, the benefit of a healthy diet on Aβ modulation is greatest when paired with hi-PA. Exercise may thus interact with diet to alter pathological processes that ultimately modify risk of Alzheimers disease.

Novel antibody capture assay for paraffin-embedded tissue detects wide-ranging amyloid beta and paired helical filament-tau accumulation in cognitively normal older adults

Quantifying antigens in formalin‐fixed tissue is challenging and limits investigation in population‐based studies of brain aging. To address this major limitation, we have developed a new technique that we call “Histelide”: immunohistochemistry (HIST‐) and enzyme‐linked immunosorbent assay (ELISA) (‐EL‐) performed on a glass slide (‐IDE). We validated Histelide in sections of prefrontal cortex from 20 selected cases: 12 subjects with clinically and neuropathologically diagnosed Alzheimers disease (AD), either autosomal dominant or late‐onset forms, and 8 clinical and neuropathologic controls. AD cases had significantly increased amyloid beta (Aβ) peptide and paired helical filament– (PHF‐) tau per area of neocortex that was proteinase K‐sensitive, and significantly decreased amount of synaptophysin. We next investigated prefrontal cortex from 81 consecutive cases of high‐cognitive performers from the Adult Changes in Thought (ACT) study, a population‐based study of brain aging and incident dementia. As expected, latent AD was common in this group; however, our results quantified widely individually varying levels of Aβ peptides and PHF‐tau among these high‐cognitive performers. This novel approach obtains quantitative data from population‐based studies, and our initial studies with high‐cognitive performers provide important quantitative insights into latent AD that should help guide expectations from neuroimaging and prevention studies.

Cerebral Cortical Aβ42 and PHF-τ in 325 Consecutive Brain Autopsies Stratified by Diagnosis, Location, and APOE

Abstract We used a novel approach to molecular quantification in standard fixed and embedded tissue to measure amyloid &bgr; 42 (A&bgr;42) and paired helical filament-&tgr; (PHF-&tgr;) in frontal, temporal, and parietal cortices from 325 consecutive brain autopsies collected as part of a population-based study of brain aging and incident dementia in the Seattle area. We observed significant effects of APOE &egr;4 on A&bgr;42 levels in both diagnostic groups by disease stage and region. In contrast, we did not observe a significant effect of APOE &egr;4 on PHF-&tgr; levels by disease stage in any region. Levels of A&bgr;42 and PHF-&tgr; in cerebral cortex were correlated more strongly in the Dementia group, and these measures had independent explanatory power for dementia beyond those of standard neuropathologic indices. Associations between Lewy body disease and A&bgr;42 or PHF-&tgr; levels and between A&bgr;42 levels and microvascular brain injury suggested that these comorbid diseases enhanced the penetrance of Alzheimer disease. Our novel approach brings additional insights into the molecular pathogenesis of common causes of dementia and may serve as a platform for future studies pursuing associations between molecular changes in Alzheimer disease and genetic or environmental risk.

Flow cytometry analysis of synaptosomes from post-mortem human brain reveals changes specific to Lewy Body and Alzheimer’s Disease

Synaptic dysfunction is thought to have an important role in the pathophysiology of neurodegenerative diseases, such as Alzheimer’s disease (AD) and Lewy body disease (LBD). To improve our understanding of synaptic alterations in health and disease, we investigated synaptosomes prepared from post-mortem human cerebral cortex, putamen (PT), and two regions of the caudate nucleus, dorso-lateral (DL) and ventro-medial (VM), regions commonly affected in AD and LBD. We observed that the fraction of synaptosomal particles with reactivity for dopamine transporter (DAT) was significantly reduced in the PT and VM caudate of patients with neuropathological diagnosis of LBD. As expected, these differences also were reflected in direct measurements of dopamine (DA) and its metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), in caudate and PT of LBD patients. The fraction of synaptosomal particles positive for amyloid β (Aβ) was significantly increased in frontal cortical samples of patients with the neuropathological diagnosis of severe AD, and was positively correlated with disease progression. We also prepared synaptosomes from the striatum of mice with severe loss of DA neurons (Slc6a3-DTR mice) and wild-type littermate controls. We observed markedly reduced levels of DAT-positive synaptosomes in Slc6a3-DTR mice following exposure to diphtheria toxin (DT). Striatal levels of DA and DOPAC in Slc6a3-DTR mice also were reduced significantly following DT exposure. We conclude that flow cytometric analysis of synaptosomes prepared from human or mouse brain provides an opportunity to study expression of pathology-associated proteins and also the specific loss of dopaminergic nerve terminals. Hence, we believe it is a valid method to detect pathological changes at the level of the synapse in LBD as well as AD.

Partial depletion of striatal dopamine enhances penetrance of cognitive deficits in a transgenic mouse model of Alzheimer's disease.

Parkinsons disease and Alzheimers disease (AD) are recognized to coexist on a spectrum of neurodegeneration, and it has been proposed that molecular interactions among pathogenic proteins are a basis for the overlap between these two diseases. We instead hypothesized that degeneration of the nigrostriatal dopaminergic system enhances the clinical penetrance of early‐stage AD. To determine the effect of striatal dopamine (DA) on the pathological effects in an experimental model of AD, APPSWE/PS1ΔE9 mice received striatal injections of the neurotoxin 6‐hydroxydopamine (6OHDA). Animals were tested in a Barnes maze protocol and in a water T‐maze protocol at different ages to determine the onset of cognitive impairment. APPSWE/PS1ΔE9 mice that received 6OHDA injections showed significant impairment in Barnes maze performance at an earlier age than controls. Additionally, at 12 months of age, APPswe/PS1ΔE9 + 6OHDA mice demonstrated worse behavioral flexibility than other groups in a task‐switch phase of the water T‐maze. To determine the neuroprotective effects of dopaminergic neurotransmission against amyloid‐β42 (Aβ42) toxicity, neuronal branch order and dendrite length were quantified in primary medium spiny neuron (MSN) cultures pretreated with increasing doses of the D1 and D2 receptor agonists before being exposed to oligomerized Aβ42. Although there were no differences in Aβ peptide levels or plaque burden among the groups, in murine MSN culture dopaminergic agonists prevented a toxic response to Aβ42. Depletion of DA in the striatum exacerbated the cognitive impairment seen in a mouse model of early‐stage AD; this may be due to a protective effect of dopaminergic innervation against Aβ striatal neurotoxicity.