Alzheimer's disease (AD) is a chronic brain disorder characterized by cognitive impairment, cholinergic dysfunction, inflammation, tau and beta-amyloid pathology and vascular damage. Recent studies have shown, that high cholesterol levels are linked to the pathology of AD. The aim of our present work was to study the effects of hypercholesterolemia in adult rats. Five months after 5% cholesterol-enriched diet plasma cholesterol levels and total weight were significantly enhanced compared to controls. Spatial memory was studied in an 8-arm radial maze and cholesterol-treated rats showed an impaired learning and long-term memory. Hypercholesterolemia significantly reduced the number of cholinergic neurons in the basal nucleus of Meynert and decreased acetylcholine levels in the cortex. Nerve growth factor was only slightly enhanced in the cortex of cholesterol-treated animals. Levels of amyloid precursor protein, beta-amyloid(1–42), as well as tau and phospho-tau 181 were significantly enhanced in the cortex of cholesterol-fed rats. Hypercholesterolemia markedly increased several cerebral inflammatory markers and enhanced microglial CD11b-like immunoreactivity. Vascular density, stained by RECA-1 was not changed. However, cholesterol induced cortical microbleedings illustrated by intensive anti-rat IgG-positive spots in the cortex. In conclusion, our data demonstrate that hypercholesterolemia in rats caused memory impairment, cholinergic dysfunction, inflammation, enhanced cortical beta-amyloid and tau and microbleedings, all indications, which resemble an AD-like pathology.

There is strong evidence that vascular risk factors play a role in the development of Alzheimer's disease (AD) or vascular dementia (vaD). Ethanol (EtOH) and cholesterol are such vascular risk factors, and we recently showed that hypercholesterolemia causes pathologies similar to AD [Ullrich et al. (2010) Mol Cell Neurosci 45, 408–417]. The aim of this study was to investigate the effects of long-term (12 months) EtOH treatment (20% v/v in drinking water) alone or long-term 5% cholesterol diet alone or a combination (mix) in adult Sprague–Dawley rats. Long-term EtOH treatment (plasma EtOH levels 58±23 mg/dl) caused significant impairment of spatial memory, reduced the number of choline acetyltransferase- and p75 neurotrophin receptor-positive nucleus basalis of Meynert neurons, decreased cortical acetylcholine, elevated cortical monocyte chemoattractant protein-1 and tissue-type plasminogen activator, enhanced microglia, and markedly induced anti-rat immunoglobulin G-positive blood–brain barrier leakage. The effect of long-term hypercholesterolemia was similar. Combined long-term treatment of rats with 20% EtOH and 5% cholesterol (mix) did not potentiate treatment with EtOH alone, but instead counteracted some of the EtOH-associated effects. In conclusion, our data show that vascular risk factors EtOH and cholesterol play a role in cognitive impairment and possibly vaD.

Hyperhomocysteinaemia (HHcy) has been identified as a cardiovascular risk factor for neurodegenerative brain diseases. The aim of the present study was to investigate the effects of short (5 months) or long (15 months) HHcy in Sprague–Dawley rats in vivo. Short- and long-term HHcy differentially affected spatial memory as tested in a partially baited eight-arm radial maze. HHcy significantly reduced the number of choline acetyltransferase (ChAT)-positive neurons in the basal nucleus of Meynert and ChAT-positive axons in the cortex only after short-term but not long-term treatment, while acetylcholine levels in the cortex were decreased at both time points. Nerve growth factor (NGF) was significantly enhanced in the cortex only after 15 months of HHcy. HHcy did not affect cortical levels of amyloid precursor protein, beta-amyloid(1-42), tau and phospho-tau181 and several inflammatory markers, as well as vascular RECA-1 and laminin density. However, HHcy induced cortical microbleedings, as illustrated by intensive anti-rat IgG-positive spots in the cortex. In order to study the regulation of the key enzyme ChAT, organotypic rat brain slices were incubated with homocysteine, which induced a decline of ChAT that was counteracted by NGF treatment. In conclusion, our data demonstrate that chronic short- and long-term HHcy differentially caused memory impairment, cholinergic dysfunction, NGF expression and vascular microbleedings.

Alzheimer's disease is a progressive brain disorder which is neuropathologically characterized by an increased number of beta-amyloid plaques, tau pathology and synapse loss. Recent research suggests that vascular pathology may be also important for the development and progression of Alzheimer's disease. It is still unknown whether there is a relation between damage of brain capillary endothelial cells (BCEC) and subsequent cholinergic cell death. The aim of this study was to examine the effects of acidosis on cell death of BCEC and cholinergic neurons in an organotypic brain slice model. We show that BCEC were heavily damaged in medium at pH<6.6. Cholinergic neurons incubated in medium pH 6.0 degenerated within 2-3 days and were not rescued by nerve growth factor (NGF). Lactate did not affect the survival of BCEC or cholinergic neurons. Both BCEC and cholinergic cells were not affected at pH 7.4, 7.0 or 6.6. It is concluded that both endothelial cells and cholinergic neurons have a high capacity to compensate for pH changes. At a certain pH, however, the vascular and neuronal cells show the same vulnerability, indicating that a low pH is deleterious for the cerebral microenvironment. Future studies are necessary to explore whether temporary pH changes could be responsible for cerebrovascular damage and cholinergic cell death. Acidosis may play an important role in the development of vascular dementia and Alzheimer's disease.

Inflammation is a hallmark in many neurodegenerative diseases like Alzheimer's disease or vascular dementia. Cholesterol and homocysteine are both vascular risk factors which have been associated with dementia, inflammation and blood–brain barrier dysfunction. In previous studies we found that hypercholesterolemia but not hyperhomocysteinemia induced inflammation in rats in vivo. The aim of the present study was to investigate the effect of a combined treatment of Sprague Dawley rats with cholesterol and homocysteine for 5 months on spatial learning and memory, blood–brain barrier integrity and inflammation. Cholesterol treated rats showed severe learning deficits, while rats treated with cholesterol and homocysteine (Mix) counteracted the cholesterol-induced inflammation and partly the cortical blood–brain barrier disruptions, although cognition was still impaired. To study the potential protective effect of homocysteine, inflammation was induced in organotypic rat brain cortex slices and primary microglial cells by treatment with different inflammatory stimuli (e.g. lipopolysaccharide or tissue plasminogen activator). Tissue plasminogen activator-induced inflammation was counteracted by homocysteine. In conclusion, our data demonstrate that homocysteine significantly ameliorates cholesterol-induced inflammation and blood–brain barrier disruption but not the memory impairment, possibly involving a tissue plasminogen activator-related mechanism.