Dietary high cholesterol and trace metals in the drinking water increase levels of ABCA1 in the rabbit hippocampus and temporal cortex.

BACKGROUND: Cholesterol-fed rabbits have been documented to show increased amyloid-ß (Aß) deposits in the brain that can be exacerbated by the quality of drinking water especially if rabbits drink tap water or distilled water containing copper. One mechanism of cholesterol and Aß clearance may be through the ATP-binding cassette transporter A1 (ABCA1). OBJECTIVE AND METHODS: Using an ABCA1 antibody, we determined the number of ABCA1-immunopositive neurons in three areas of rabbit brain as a function of feeding 2% cholesterol and providing tap water, distilled water, or distilled water to which aluminum, copper, or zinc was added. RESULTS: The number of neurons with ABCA1 immunoreactivity was increased significantly as a result of dietary cholesterol in the rabbit hippocampus and inferior and superior temporal cortex. The number of neurons with ABCA1 immunoreactivity was further increased in all three areas as a result of cholesterol-fed rabbits drinking tap water or distilled water with copper. Finally, cholesterol-fed rabbits that drank distilled water with aluminum also showed an increased number of ABCA1-immunopositive neurons in inferior and superior temporal cortex. CONCLUSIONS: These data suggest that ABCA1 levels increase in parallel with previously documented increases in Aß levels as a result of high dietary cholesterol and copper in the drinking water. Addition of aluminum to distilled water may have a similar effect in the temporal cortex. ABCA1 has been proposed as a means of clearing Aß from the brain and manipulations that increase Aß also result in an increase of clearance machinery.

KIF6 719Arg allele is associated with statin effects on cholesterol levels in amnestic mild cognitive impairment and Alzheimer's disease patients.

KIF6 719Arg allele carriers are thought to have a greater lipid lowering response from statin therapy than non-carriers. Given the continued interest in the relationship between cholesterol, statin use, amnestic mild cognitive impairment (aMCI), and Alzheimer's disease (AD), investigating the role of KIF6 719Arg carrier status in these relationships may be of importance. Data from 86 patients (36 aMCI, 50 AD) with an average age of 76.87 ± 8.22 years were used for this study. Total cholesterol (TC), low density lipoprotein (LDL), high density lipoprotein (HDL), and triglycerides were the outcome variables. 719Arg carriers taking statins had significantly lower TC (p < 0.001) and LDL (p < 0.001) levels than 719Arg carriers not taking statins. In addition, 719Arg carriers not taking statins had significantly higher TC (p = 0.004) and LDL (p < 0.001) than 719Arg non-carriers taking statins. Additional analyses indicated that ApoE ε4 carrier status and statin use interaction is also associated with lower TC (p = 0.04), but not LDL (p = 0.06). The interaction between 719Arg and ApoE ε4 carrier status on TC and LDL was not significant. This study is the first to demonstrate an association between lower cholesterol levels and statin use among KIF6 719Arg allele carriers with aMCI and AD. Accounting for 719Arg carrier status may be important in future studies investigating the link between cholesterol and AD and also for AD and aMCI clinical trials using statins as a treatment.

Cholesterol increases ventricular volume in a rabbit model of Alzheimer's disease.

One of the hallmarks of Alzheimer's disease is a significant increase in ventricular volume. To date we and others have shown that a cholesterol-fed rabbit model of Alzheimer's disease displays as many as fourteen different pathological markers of Alzheimer's disease including amyloid-ß accumulation, thioflavin-S staining, blood brain barrier breach, microglia activation, cerebrovasculature changes, and alterations in learning and memory. Using structural magnetic resonance imaging at 3T, we now report that cholesterol-fed rabbits also show a significant increase in ventricular volume following 10 weeks on a diet of 2% cholesterol. The increase in volume is attributable in large part to increases in the size of the third ventricle. These changes are accompanied by significant increases in the number of amyloid-ß immuno-positive cells in the cortex and hippocampus. Increases in the number of amyloid-ß neurons in the cortex also occurred with the addition of 0.24 ppm copper to the drinking water. Together with a list of other pathological markers, the current results add further validity to the value of the cholesterol-fed rabbit as a non-transgenic animal model of Alzheimer's disease.

Statins to treat Alzheimer's disease: an incomplete story.

The link between cholesterol and Alzheimer's disease (AD) has been explored for almost two decades. The link stems from the observation that atherosclerotic heart disease increases the risk for AD and that people expiring from coronary artery disease had AD changes in their brains. Cholesterol is a cofactor of amyloid deposition, with substantial evidence showing that high cholesterol diets in animal models can accelerate amyloidogenesis. This link led investigators to posit the use of cholesterol-lowering agents as treatments for AD and cognitive decline. Indeed, the epidemiological data suggest that cholesterol-lowering agents may reduce the risk of developing AD. Early pilot studies suggested that statins may be useful as treatments for AD because of a reduction in the rates of decline. Recent reports of simvastatin and atorvastatin assessed in large randomized, double-blind, placebo-controlled multicenter trials have not confirmed a clinically demonstrable cognitive benefit for statins in the treatment of AD. This article will discuss the results of one of these trials and explore the reasons behind why the multicenter trials may not have been positive and the growing disparity between preclinical/epidemiological benefit and a lack of clinical efficacy.

Tau is reduced in AD plasma and validation of employed ELISA methods.

OBJECTIVE: Measure total tau levels in the circulation of living humans, validate the methods employed and determine if there are consistent differences in total tau levels between normal controls and individuals with mild cognitive impairment (MCI) and/or Alzheimer's disease (AD). METHODS: Employing ELISA methods, validated by Western bolts using three separate tau antibodies, we quantified total tau levels in serially collected serum and plasma samples from individuals longitudinally evaluated for cognitive performance. RESULTS: We identified substantial levels of tau in human circulation using plasma, but not serum. The measurement of authentic tau protein was verified by Western blots using a C-terminal specific antibody, an N-terminal specific antibody and antibody used in the commercially available ELISA kit. We revealed a significant decrease in plasma levels of total tau among subjects with MCI compared to cognitively normal controls, with a further highly significant reduction in AD patients compared to both MCI and normal controls. We also found a significant positive correlation between changing levels of plasma tau and cognitive performance within the entire population and among AD patients. CONCLUSIONS: The data suggest that changes in circulating tau levels quantified in plasma samples, but not serum samples, may represent a viable biomarker for tracking the progression of AD and the efficacy of medications in its treatment.

Influence of water quality on cholesterol-induced tau pathology: preliminary data.

The studies employed the cholesterol-fed rabbit model of Alzheimer's disease (AD) to investigate the relationship between AD-like neurofibrillary tangle (NFT) neuropathology and tau protein levels as the main component of NFT. We measured brain and plasma tau levels and semiquantified NFT-like neuropathology in cholesterol-fed rabbits administered drinking water of varying quality (distilled, tap, and distilled+copper) compared to animals receiving normal chow and local tap water. Total tau levels in plasma were increased in all cholesterol-fed rabbits compared to animals on normal chow, regardless of quality of water. In contrast, increased tau in brain and increased AT8 immunoreactive NFT-like lesions were greatest in cholesterol-fed rabbits administered distilled water. A substantial decrease in brain tau and incidence and density of AT8 immunoreactive NFT-like lesions occurred in cholesterol-fed rabbits administered copper water, and an even greater decrease was observed in cholesterol-fed animals on local tap water. These studies suggest the possibility that circulating tau could be the source of the tau accumulating in the brain.

Neurovascular changes measured by time-of-flight MR angiography in cholesterol-fed rabbits with cortical amyloid beta-peptide accumulation.

PURPOSE: To test the hypothesis that narrowing of cranial blood vessels in cholesterol-fed rabbits is a function of the duration of the high cholesterol diet. Such neurovascular changes, caused by elevated serum cholesterol, are linked to stroke and Alzheimer's disease risk. MATERIALS AND METHODS: Four groups of New Zealand White rabbits were studied. Six were fed a normal diet, 19 were fed a 2% cholesterol diet with 0.12 ppm copper in the drinking water for 8 weeks, 10 weeks, or 12 weeks. Time-of-flight (TOF) MR angiography (MRA) at 3 Tesla was used to measure arterial diameters in 11 vessels. Previously published data for amyloid beta-peptide (Abeta) accumulation in the brains measured postmortem were correlated to vessel diameters. Ventricular volumes of rabbits were measured on group-averaged data. RESULTS: Several vessel diameters decreased with cholesterol diet duration. The posterior communicating arteries showed the largest significant effect. Abeta accumulation was inversely correlated with arterial diameter. Ventricular volumes between the normal diet and 12 weeks cholesterol-fed groups were not significantly different. CONCLUSION: Reduction in vessel diameter of medium-sized vessels but not large vessels was measured in these hypercholesterolemic rabbits. The vessel diameter narrowing and cortical Abeta deposition occurred before measurable ventricular enlargement.

Cholesterol and cognitive performance in normal controls and the influence of elective statin use after conversion to mild cognitive impairment: results in a clinical trial cohort.

BACKGROUND: We reported a significant 67% reduction in the hazard risk of incident Alzheimer's disease (AD) with elective statin use in the AD Anti-inflammatory Prevention Trial (ADAPT), without a reduction in risk of incident mild cognitive impairment (MCI). OBJECTIVE: To assess if cholesterol levels are associated with cognitive performance and determine if statin use alters cognitive performance after onset of MCI. DESIGN: Fractionated cholesterol levels, neurological and cognitive status were evaluated annually. Comparisons of non-LLA (lipid-lowering agent) users or statin-LLA users were performed blind to the ADAPT medication randomization. Pearson's correlations were validated using a time-dependent linear mixed model. RESULTS: The MMSE performance significantly declined over time in non-LLA users, and, after adjusting for this, a significant positive correlation between MMSE and HDL was identified (p = 0.0002). A negative correlation between total and LDL cholesterol, and immediate and delayed recall of the Rivermead paragraph was significant (total cholesterol, p < 0.003; LDL, p < 0.02). Pilot data suggest a positive signal on delayed recall of both the Hopkins word list and Rivermead paragraph with deterioration in the non-LLA users and improvement in the statin users after conversion to MCI. CONCLUSION: Cholesterol levels may be associated with differential performance on the MMSE and measures of learning or memory. The trend for improved delayed recall in statin users with MCI compared to non-LLA users with MCI may have contributed to the reduced hazards risk of incident AD without reducing the risk of MCI.

Angiotensin I-converting enzyme I/D polymorphism and suicidal behaviors.

Suicide is one of the ten most common causes of death in Western countries. It involves genetic vulnerability factors and is often associated with major depression. A Japanese team reported an association between the insertion allele of the angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphism with completed suicide. The ACE I/D polymorphism was investigated in two independent case-control studies, one involving 64 suicide completers and 90 controls who all underwent forensic investigations, the second one consisting of 588 suicide attempters and 639 controls. In the two population samples studied a statistically significant risk of suicidal behavior was observed for subjects bearing the DD genotype. These results suggest a possible role of the renin-angiotensin system in suicidal behavior.

The early and ongoing experience with the cholesterol-fed rabbit as a model of Alzheimer's disease: the old, the new and the pilot.

Pioneering autopsy studies revealed a possible link between coronary artery disease, cholesterol and Alzheimer's disease (AD). In the cholesterol-fed rabbit model of human coronary artery disease, we identified numerous neuropathologic features of AD including central accumulation of amyloid-beta (Abeta) and cognitive deficits compared to rabbits fed unaltered diet. Removing cholesterol from the diet or treatment with cholesterol-lowering medications reversed the severity of AD-like alterations. This fostered the rationale for testing a cholesterol-lowering statin medication for benefit in the treatment of AD. Further studies suggested that the cholesterol-fed rabbit was a viable model for AD, but the severity of the neuropathology produced exhibited gender-related differences. Furthermore the induction of AD-like neuropathology by dietary cholesterol was found to depend on the quality of water the animal was drinking. Cholesterol-fed rabbits drinking distilled water showed minimal central changes, whereas animals drinking distilled water supplemented with low levels of copper were severely affected. It was clear that cholesterol caused the over-production of Abeta in the brain and copper influenced its clearance to the blood. Emerging data suggest that low-density lipoprotein receptor-related protein-1 (LRP) on brain capillaries clears Abeta from brain and that excess circulating copper negatively influences this process.

Reduced risk of incident AD with elective statin use in a clinical trial cohort.

Statins have been reported to reduce the risk and be of benefit in the treatment of Alzheimer's disease (AD). Individuals enrolling in the randomized controlled trial testing two anti-inflammatory agents for primary prevention of AD (Alzheimer's Disease Anti-inflammatory Prevention Trial; ADAPT) were allowed the elective use of statins. Our objective was to assess whether statin use is associated with reduced risk of incident AD among ADAPT participants. In primary ADAPT study , participants were assessed annually for cholesterol levels and cognitive status. If impairment in cognition was noted, a dementia evaluation was performed. Onset of mild cognitive impairment (MCI) or AD was taken as the date of this evaluation. Time-to-onset was analyzed in six-month intervals following enrollment. Without knowledge of primary treatment assignment in ADAPT, participants were grouped by their self-reported use of lipid-lowering agents (LLA). In the current ancillary ADAPT study we found that elective statin use was associated with significantly reduced risk of incident AD after adjustment for age, gender, education and Apolipoprotein E (ApoE) genotype. The findings were similar when comparing all LLA use (statin and non-statin LLA) to non-LLA use. Cholesterol levels were lower among statin users compared with non-LLA users, but the MMSE scores were equivalent. The data suggest that statin therapy may be of benefit in reducing the risk of AD.

Hippocampal volume change in the Alzheimer Disease Cholesterol-Lowering Treatment trial.

Numerous clinical studies suggest a link between elevated cholesterol and increased risk of Alzheimer disease (AD), and the preponderance of data suggests that statin therapy may reduce the risk of AD later in life. The first clinical investigation of statin therapy in patients with AD, the AD Cholesterol-Lowering Treatment (ADCLT) trial, found that atorvastatin 80 mg/day was associated with improvements relative to placebo on some, but not all, cognitive measures after 6 months and 1 year of therapy. We report here findings from a pilot ADCLT substudy showing a nonsignificant reduction in total hippocampal volume with 1 year of atorvastatin therapy compared with placebo, driven by a highly significant reduction in right hippocampal volume with atorvastatin therapy.

Microglial dystrophy in the aged and Alzheimer's disease brain is associated with ferritin immunoreactivity.

Degeneration of microglial cells may be important for understanding the pathogenesis of aging-related neurodegeneration and neurodegenerative diseases. In this study, we analyzed the morphological characteristics of microglial cells in the nondemented and Alzheimer's disease (AD) human brain using ferritin immunohistochemistry. The central hypothesis was that expression of the iron storage protein ferritin increases the susceptibility of microglia to degeneration, particularly in the aged brain since senescent microglia might become less efficient in maintaining iron homeostasis and free iron can promote oxidative damage. In a primary set of 24 subjects (age range 34-97 years) examined, microglial cells immunoreactive for ferritin were found to constitute a subpopulation of the larger microglial pool labeled with an antibody for HLA-DR antigens. The majority of these ferritin-positive microglia exhibited aberrant morphological (dystrophic) changes in the aged and particularly in the AD brain. No spatial correlation was found between ferritin-positive dystrophic microglia and senile plaques in AD tissues. Analysis of a secondary set of human postmortem brain tissues with a wide range of postmortem intervals (PMI, average 10.94 +/- 5.69 h) showed that the occurrence of microglial dystrophy was independent of PMI and consequently not a product of tissue autolysis. Collectively, these results suggest that microglial involvement in iron storage and metabolism contributes to their degeneration, possibly through increased exposure of the cells to oxidative stress. We conclude that ferritin immunohistochemistry may be a useful method for detecting degenerating microglia in the human brain.

Classical conditioning of the rabbit's nictitating membrane response is a function of the duration of dietary cholesterol.

Modifying dietary cholesterol may improve learning and memory but very high cholesterol can cause pathophysiology and death. Rabbits fed 2% cholesterol for 8, 10 or 12 weeks with 0.12 ppm copper added to distilled water and rabbits fed a normal diet without copper added to distilled water (0 weeks) were given a difficult trace classical conditioning task and an easy delay conditioning task pairing tone with corneal air puff. The majority of cholesterol-fed rabbits survived the deleterious effects of the diet but survival was an inverse function of the diet duration. Compared to controls, the level of classical conditioning and conditioning-specific reflex modification were an inverted "U"-shaped function of diet duration. Highest levels of responding occurred in rabbits on cholesterol for 10 weeks and trace conditioning was negatively correlated with the number of hippocampal beta-amyloid-positive neurons. Rabbits on the diet for 12 weeks responded at levels comparable to controls. The data provide support for the idea that dietary cholesterol may facilitate learning and memory but there is an eventual trade off with pathophysiological consequences of the diet.

Classification and prediction of clinical Alzheimer's diagnosis based on plasma signaling proteins.

A molecular test for Alzheimer's disease could lead to better treatment and therapies. We found 18 signaling proteins in blood plasma that can be used to classify blinded samples from Alzheimer's and control subjects with close to 90% accuracy and to identify patients who had mild cognitive impairment that progressed to Alzheimer's disease 2-6 years later. Biological analysis of the 18 proteins points to systemic dysregulation of hematopoiesis, immune responses, apoptosis and neuronal support in presymptomatic Alzheimer's disease.

Microglial activation in the hippocampus of hypercholesterolemic rabbits occurs independent of increased amyloid production.

BACKGROUND: Rabbits maintained on high-cholesterol diets are known to show increased immunoreactivity for amyloid beta protein in cortex and hippocampus, an effect that is amplified by presence of copper in the drinking water. Hypercholesterolemic rabbits also develop sporadic neuroinflammatory changes. The purpose of this study was to survey microglial activation in rabbits fed cholesterol in the presence or absence of copper or other metal ions, such as zinc and aluminum. METHODS: Vibratome sections of the rabbit hippocampus and overlying cerebral cortex were examined for microglial activation using histochemistry with isolectin B4 from Griffonia simplicifolia. Animals were scored as showing either focal or diffuse microglial activation with or without presence of rod cells. RESULTS: Approximately one quarter of all rabbits fed high-cholesterol diets showed evidence of microglial activation, which was always present in the hippocampus and not in the cortex. Microglial activation was not correlated spatially with increased amyloid immunoreactivity or with neurodegenerative changes and was most pronounced in hypercholesterolemic animals whose drinking water had been supplemented with either copper or zinc. Controls maintained on normal chow were largely devoid of neuroinflammatory changes, but revealed minimal microglial activation in one case. CONCLUSION: Because the increase in intraneuronal amyloid immunoreactivity that results from administration of cholesterol occurs in both cerebral cortex and hippocampus, we deduce that the microglial activation reported here, which is limited to the hippocampus, occurs independent of amyloid accumulation. Furthermore, since neuroinflammation occurred in the absence of detectable neurodegenerative changes, and was also not accompanied by increased astrogliosis, we conclude that microglial activation occurs because of metabolic or biochemical derangements that are influenced by dietary factors.

High dietary cholesterol facilitates classical conditioning of the rabbit's nictitating membrane response.

Studies have shown that modifying dietary cholesterol may improve learning and that serum cholesterol levels can be positively correlated with cognitive performance. Rabbits fed a 0, 0.5, 1 or 2% cholesterol diet for eight weeks and 0.12 ppm copper added to their drinking water received trace and then delay classical conditioning pairing tone with corneal air puff during which movement of the nictitating membrane (NM) across the eye was monitored. We found that the level of classical conditioning and conditioning-specific reflex modification (CRM) as well as the number of beta amyloid-labeled neurons in the cortex and hippocampus were a function of the concentration of cholesterol in the diet. The data provide support for the idea that dietary cholesterol may facilitate learning and memory.

Cholesterol enhances classical conditioning of the rabbit heart rate response.

The cholesterol-fed rabbit is a model of atherosclerosis and has been proposed as an animal model of Alzheimer's disease. Feeding rabbits cholesterol has been shown to increase the number of beta amyloid immunoreactive neurons in the cortex. Addition of copper to the drinking water of cholesterol-fed rabbits can increase this number still further and may lead to plaque-like structures. Classical conditioning of the nictitating membrane response in cholesterol-fed rabbits is retarded in the presence of these plaque-like structures but may be facilitated in their absence. In a factorial design, rabbits fed 2% cholesterol or a normal diet (0% cholesterol) for 8 weeks with or without copper added to the drinking water were given trace classical conditioning using a tone and periorbital electrodermal stimulation to study the effects of cholesterol and copper on classical conditioning of heart rate and the nictitating membrane response. Cholesterol-fed rabbits showed significant facilitation of heart rate conditioning and conditioning-specific modification of heart rate relative to normal diet controls. Consistent with previous research, cholesterol had minimal effects on classical conditioning of the nictitating membrane response when periorbital electrodermal stimulation was used as the unconditioned stimulus. Immunohistochemical analysis showed a significant increase in the number of beta amyloid positive neurons in the cortex, hippocampus and amygdala of the cholesterol-fed rabbits. Supplementation of drinking water with copper increased the number of beta amyloid positive neurons in the cortex of cholesterol-fed rabbits but did not produce plaque-like structures or have a significant effect on heart rate conditioning. The data provide additional support for our finding that, in the absence of plaques, dietary cholesterol may facilitate learning and memory.