Alzheimer’s Disease and Cholesterol: The Fat Connection

Raman signature from brain hippocampus could aid Alzheimer's disease diagnosis

Micro-Raman spectroscopy (MRS) is used for the first time to our knowledge to investigate brain hippocampus tissue from Alzheimer's disease (AD) infected rats. In situ Raman analysis of tissue sections provides distinct spectra useful for distinguishing AD from normal state. The biochemical changes of brain hippocampus tissue including the deposit of beta-amyloid (Abeta) protein, the increase of cholesterol, and hyperphosphorylated tau are observed through MRS when AD occurs. A more convincing multi-Raman criterion based on single Raman peaks, and further in combination with statistical analysis of the entire Raman spectrum, is found capable of classifying brain hippocampus tissues with different pathological features. This study demonstrates the brain hippocampus is an important candidate for considering the early pathological state of AD, and Raman signatures from the brain hippocampus could aid AD diagnosis. In addition, Raman results undoubtedly confirm simultaneous changes of cholesterol and Abeta in the progression of AD.

Polar metabolite of cholesterol induces rat cognitive dysfunctions

24-hydroxycholesterol, a major polar metabolite of brain cholesterol, has neurotoxic effects. However, little is known about the effects of this polar metabolite on the CNS. In the present study, the effects of 24-hydroxycholesterol on behavior changes were investigated. Rats were divided into three groups: (i) a control group; (ii) a sham group: 0.5 ml PBS was infused into the cerebral ventricle; (iii) a model group: 0.5 ml 24-hydroxycholesterol (10 microM) was infused into the cerebral ventricle. 24-hydroxycholesterol can obviously impair rats' acquisition and probe trial in the Morris Water Maze task. Compared with rats in the sham group, rats in the model group had longer escape latency time and traveled more distance, and performed worse in the probe trial task manifested by spending less time in the annulus and training quadrant, which probably was attributed to the neuronal degeneration in hippocampal CA1 area induced by 24-hydroxycholesterol as examined by histological assay and apoptotic assay. Our results revealed that the polar metabolites, such as 24-hydroxycholesterol, exert neurotoxic effects and exacerbate the neuron injury with their abnormal accumulation. These findings suggest that measures taken promptly to eliminate or inhibit the accumulation of polar metabolites should be a potential strategy to prevent neurological dysfunctions and promote the recovery of functional deficits after neurotoxic insult.

Clinical field-strength MRI of amyloid plaques induced by low-level cholesterol feeding in rabbits

Two significant barriers have limited the development of effective treatment of Alzheimer's disease. First, for many cases the aetiology is unknown and likely multi-factorial. Among these factors, hypercholesterolemia is a known risk predictor and has been linked to the formation of β-amyloid plaques, a pathological hallmark this disease. Second, standardized diagnostic tools are unable to definitively diagnose this disease prior to death; hence new diagnostic tools are urgently needed. Magnetic resonance imaging (MRI) using high field-strength scanners has shown promise for direct visualization of β-amyloid plaques, allowing in vivo longitudinal tracking of disease progression in mouse models. Here, we present a new rabbit model for studying the relationship between cholesterol and Alzheimer's disease development and new tools for direct visualization of β-amyloid plaques using clinical field-strength MRI. New Zealand white rabbits were fed either a low-level (0.125–0.25% w/w) cholesterol diet (n = 5) or normal chow (n = 4) for 27 months. High-resolution (66 × 66 × 100 µm³; scan time = 96 min) ex vivo MRI of brains was performed using a 3-Tesla (T) MR scanner interfaced with customized gradient and radiofrequency coils. β-Amyloid-42 immunostaining and Prussian blue iron staining were performed on brain sections and MR and histological images were manually registered. MRI revealed distinct signal voids throughout the brains of cholesterol-fed rabbits, whereas minimal voids were seen in control rabbit brains. These voids corresponded directly to small clusters of extracellular β-amyloid-positive plaques, which were consistently identified as iron-loaded (the presumed source of MR contrast). Plaques were typically located in the hippocampus, parahippocampal gyrus, striatum, hypothalamus and thalamus. Quantitative analysis of the number of histologically positive β-amyloid plaques (P < 0.0001) and MR-positive signal voids (P < 0.05) found in cholesterol-fed and control rabbit brains corroborated our qualitative observations. In conclusion, long-term, low-level cholesterol feeding was sufficient to promote the formation of extracellular β-amyloid plaque formation in rabbits, supporting the integral role of cholesterol in the aetiology of Alzheimer's disease. We also present the first evidence that MRI is capable of detecting iron-associated β-amyloid plaques in a rabbit model of Alzheimer's disease and have advanced the sensitivity of MRI for plaque detection to a new level, allowing clinical field-strength scanners to be employed. We believe extension of these technologies to an in vivo setting in rabbits is feasible and that our results support future work exploring the role of MRI as a leading imaging tool for this debilitating and life-threatening disease.

Effects of hypertension and hypercholesterolemia on cognitive functioning in patients with alzheimer disease

This study investigated the relationship between the vascular comorbidities (VCs) of hypertension and hypercholesterolemia and the cognitive phenotype of Alzheimer disease (AD). Seventy-four AD patients underwent objective measurement of blood pressure and serum cholesterol levels, and they received a detailed neuropsychologic evaluation examining attention, memory, language, visuomotor/visuospatial skills, and executive functioning. Multiple regression analyses controlling for demographic variables, overall cognitive status, and the presence of diabetes/cardiac disease indicated that an increase in the number of VCs, but not their severity, was associated with poorer verbal and visual recall, visuoconstructive and spatial analysis, verbal reasoning, and set shifting. The findings demonstrate that VCs are associated with specific aspects of cognitive functioning in AD patients. The mechanisms likely involve the effects of VCs on cerebrovascular disease including white matter disruption. The results highlight the importance of controlling these risk factors in patients who carry the diagnosis of AD.

Fatty acids, lipid metabolism and Alzheimer pathology

Alzheimer's disease is the most common form of dementia in the elderly. The cause of Alzheimer's disease is still unknown and there is no cure for the disease yet despite 100 years of extensive research. Cardiovascular risk factors such as high serum cholesterol, presence of the Apolipoprotein epsilon4 (APOE epsilon4) allele and hypertension, play important roles in the development of Alzheimer's disease. We postulate that a combination of diet, lifestyle, vascular, genetic, and amyloid related factors, which enhance each other's contribution in the onset and course of Alzheimer's disease, will be more likely the cause of the disease instead of one sole mechanism. The possibility that the risk for Alzheimer's disease can be reduced by diet or lifestyle is of great importance and suggests a preventative treatment in Alzheimer's disease. Because of the great importance of lipid diets and metabolism in preventative treatment against both Alzheimer's disease and cardiovascular disease, long-chain polyunsaturated fatty acids from fish oil, ApoE genotype and cholesterol metabolism in correlation with Alzheimer's disease will be reviewed.

Mechanisms of disease: new therapeutic strategies for Alzheimer's disease--targeting APP processing in lipid rafts

Alzheimer's disease (AD) is the most common cause of age-related dementia. Pathologically, AD is characterized by the deposition in the brain of amyloid-beta peptides derived from proteolysis of amyloid precursor protein (APP) by beta-site APP cleaving enzyme 1 (BACE1) and gamma-secretase. A growing body of evidence implicates cholesterol and cholesterol-rich membrane microdomains in amyloidogenic processing of APP. Here, we review recent findings regarding the association of BACE1, gamma-secretase and APP in lipid rafts, and discuss potential therapeutic strategies for AD that are based on knowledge gleaned from the membrane environment that fosters APP processing.

Targeting age-related macular degeneration with Alzheimer's disease based immunotherapies: anti-amyloid-beta antibody attenuates pathologies in an age-related macular degeneration mouse model

Age-related macular degeneration (AMD) is a late-onset, neurodegenerative retinal disease that shares several clinical and pathological features with Alzheimer's disease (AD) including extracellular deposits containing amyloid-beta (Abeta) peptides. Immunotherapy targeting the Abeta protein has been investigated as a potential treatment for AD. Here, we present the rationale for extending this approach to treat AMD. We tested an anti-Abeta antibody administered systemically in a mouse model of AMD. Histological and functional measurements in treated animals compared to controls showed that following immunotherapy, the amounts of Abeta in the retina and brain were decreased and the ERG deficits in the retina were attenuated. These data support the hypothesis that Abeta is a therapeutic target for AMD.