Karin M. Thelen

High-dose statins and skeletal muscle metabolism in humans: A randomized, controlled trial

Myopathy, probably caused by 3‐hydroxy‐3‐methylglutaryl‐coenzyme A reductase inhibition in skeletal muscle, rarely occurs in patients taking statins. This study was designed to assess the effect of high‐dose statin treatment on cholesterol and ubiquinone metabolism and mitochondrial function in human skeletal muscle.

Brain Cholesterol Synthesis in Mice Is Affected by High Dose of Simvastatin but Not of Pravastatin

On a global scale, there is an increasing tendency for a more aggressive treatment of hypercholesterolemia. Minor effects of statins on brain cholesterol metabolism have been reported in some in vivo animal studies, and it seems that this is due to a local effect of the drug. We treated male mice of the inbred strain C57/BL6 with a high daily dose of lipophilic simvastatin (100 mg/kg b.wt.) or hydrophilic pravastatin (200 mg/kg b.wt.) or vehicle (controls) by oral gavage for 3 days. To compare the impact of both statins on brain cholesterol synthesis and degradation, levels of cholesterol, its precursor lathosterol, and its brain metabolite 24(S)-hydroxycholesterol as well as statin concentrations were determined in whole-brain lipid extracts using mass spectrometry. The expression of 3-hydroxy-3-methylglutaryl (HMG)-coenzyme A (CoA) reductase mRNA and of other target genes were evaluated using real-time reverse transcription-polymerase chain reaction. In addition, analysis of liver and serum samples was performed. Similar levels of simvastatin and pravastatin were detected in whole-brain homogenates. Cholesterol contents in the brain, liver, and serum were not affected by high-dose statin treatment. Whereas brain cholesterol precursor levels were reduced in simvastatin-treated animals only, no effect was observed on the formation of the brain cholesterol metabolite, 24(S)-hydroxycholesterol. Polymerase chain reaction analysis revealed that mRNA expression of HMG-CoA reductase and ATP-binding cassette transporter A1 in the brain was significantly up-regulated in simvastatin-treated animals compared with pravastatin-treated or control animals. We conclude that, under the present experimental conditions, brain cholesterol synthesis is significantly affected by short-term treatment with high doses of lipophilic simvastatin, whereas whole-brain cholesterol turnover is not disturbed.

The role of seladin‐1/DHCR24 in cholesterol biosynthesis, APP processing and Aβ generation in vivo

The cholesterol‐synthesizing enzyme seladin‐1, encoded by the Dhcr24 gene, is a flavin adenine dinucleotide‐dependent oxidoreductase and regulates responses to oncogenic and oxidative stimuli. It has a role in neuroprotection and is downregulated in affected neurons in Alzheimers disease (AD). Here we show that seladin‐1‐deficient mouse brains had reduced levels of cholesterol and disorganized cholesterol‐rich detergent‐resistant membrane domains (DRMs). This was associated with inefficient plasminogen binding and plasmin activation, the displacement of β‐secretase (BACE) from DRMs to APP‐containing membrane fractions, increased β‐cleavage of APP and high levels of Aβ peptides. In contrast, overexpression of seladin‐1 increased both cholesterol and the recruitment of DRM components into DRM fractions, induced plasmin activation and reduced both BACE processing of APP and Aβ formation. These results establish a role of seladin‐1 in the formation of DRMs and suggest that seladin‐1‐dependent cholesterol synthesis is involved in lowering Aβ levels. Pharmacological enhancement of seladin‐1 activity may be a novel Aβ‐lowering approach for the treatment of AD.

High doses of simvastatin, pravastatin, and cholesterol reduce brain cholesterol synthesis in guinea pigs.

Recent epidemiological studies suggest that inhibitors of 3-hydroxy-3-methyl-glutaryl CoA reductase, so-called statins, are effective in lowering the prevalence of Alzheimers disease. Whether the effect of statins is due to a local inhibition of cholesterol synthesis in the brain or whether it is mediated by the reduced levels of cholesterol in the circulation is not known. In the present work, we tested the possibility that high doses of lipophilic and hydrophilic statins, simvastatin and pravastatin, respectively, or a diet high in cholesterol could affect cholesterol homeostasis in the brain of guinea pigs. The total brain cholesterol levels were not affected by high-dose simvastatin or pravastatin treatment. Significantly lower levels of the cholesterol precursor lathosterol and its ratio to cholesterol were found in the brains of simvastatin and pravastatin-treated animals. 24S-Hydroxycholesterol, the transportable form of cholesterol across the blood-brain barrier, was significantly lower in the brain of pravastatin-treated animals. Excessive cholesterol feeding resulted in higher serum cholesterol levels but did not affect total brain cholesterol level. However, de novo cholesterol synthesis in the brain seemed to be down-regulated, as indicated by lower absolute levels and cholesterol-related ratios of lathosterol compared with controls. The passage of deuterium-labeled cholesterol across the blood-brain barrier in one animal was found to be approximately 1%. Our results suggest that brain cholesterol synthesis in guinea pigs can be slightly, but significantly, influenced by high doses of lipophilic and hydrophilic statins as well as by high dietary cholesterol intake, while total brain cholesterol content and thus, cholesterol homeostasis is maintained.

Polymorphisms in glutathione S-transferase omega-1 and AD, vascular dementia, and stroke.

Background: Glutathione S-transferase omega-1 (GSTO1) protects from oxidative stress, a risk factor for Alzheimer disease (AD), vascular dementia (VaD), and stroke. Polymorphisms in GSTO1 might influence the function of the protein and thus the risk of AD, VaD, and stroke. Methods: The GSTO1 gene was screened for variations. The effect of the detected polymorphisms on the risk of AD, VaD, and stroke was evaluated. CSF levels of cholesterol and plasma homocysteine levels were compared according to the GSTO1 genotype. Results: Two missense polymorphisms in exon 4 of GSTO1 (Ala140Asp and Glu155ΔGlu) were detected and tested for their association with AD, VaD, and stroke. The Asp/Asp and Ala/Asp genotypes increased the risk of stroke (p = 0.003, OR = 2.1), and the Asp/Asp genotype increased the risk of VaD (p = 0.02, OR = 2.2). GSTO1 polymorphisms did not influence the risk of AD, but the Asp allele influenced the age at onset (p = 0.05). In nondemented probands CSF levels of cholesterol were increased in carriers of the Asp/Asp genotype (p = 0.004); however, in patients with manifest dementia the authors found decreased CSF levels of cholesterol in carriers of the Asp/Asp genotype (p = 0.028). Serum homocysteine levels in stroke patients were higher in carriers of at least one Asp allele (p = 0.011). Conclusion: The GSTO1 Asp allele may be a genetic risk factor for cerebrovascular diseases, and might influence the course of Alzheimer disease, even though effects vary in different studies.

The effect of simvastatin treatment on the amyloid precursor protein and brain cholesterol metabolism in patients with Alzheimer's disease.

During the last years, several clinical studies have been published trying to elucidate the effect of statin treatment on amyloid precursor protein (APP) processing and metabolism of brain cholesterol in Alzheimer’s disease (AD) in humans. We present an open biochemical study where 19 patients with AD have been treated with simvastatin (20 mg/day) for 12 months. The aim was to further investigate the effect of simvastatin treatment on cerebrospinal fluid (CSF) biomarkers of APP processing, AD biomarkers as total tau and tau phosphorylated at threonine 181, brain cholesterol metabolism as well as on cognitive decline in patients with AD. Despite biochemical data suggesting that treatment with 20 mg/day of simvastatin for 12 months does affect the brain cholesterol metabolism, we did not find any change in CSF or plasma levels of β-amyloid (Aβ)1–42. However, by analysis of APP isoforms, we found that statin treatment may favor the nonamyloidogenic pathway of APP processing. The relevance and mechanism between statin treatment and AD has to be further elucidated by using statins of different lipophility in different dosages over a longer period of time.

Cholesterol synthesis rate in human hippocampus declines with aging.

During the last three to four decades, interest in the interaction of circulating and brain cholesterol has increased. As the CNS matures and cholesterol pools in the brain become constant, the rate of de novo synthesis of cholesterol in the brain is expected to decline. We measured cholesterol, its precursors and its brain specific metabolite 24S-hydroxycholesterol in hippocampus from 7 female and 13 male corpses by highly sensitive and specific gas chromatography-mass spectrometry. Two age groups (young, n=10; elderly, n=10) were formed with a cut-off at the median age of 38 years. The amount of cholesterol was comparable in young and elderly subjects. The concentrations of the cholesterol precursors lanosterol and lathosterol were significantly higher in young (P=0.036 and 0.005, respectively) than in elderly subjects. In accordance, there was a significantly negative correlation between age and lathosterol concentrations (r=-0.505; P=0.023). Absolute levels of 24S-hydroxycholesterol in the brain were slightly, but not significantly, lower in the hippocampal specimens from the elderly subjects. We conclude that during aging, cholesterol synthesis is decreased in the hippocampus, while absolute cholesterol content remains at a stable level.

Loss of gamma-secretase function impairs endocytosis of lipoprotein particles and membrane cholesterol homeostasis.

Presenilins (PSs) are components of the γ-secretase complex that mediates intramembranous cleavage of type I membrane proteins. We show that γ-secretase is involved in the regulation of cellular lipoprotein uptake. Loss of γ-secretase function decreased endocytosis of low-density lipoprotein (LDL) receptor. The decreased uptake of lipoproteins led to upregulation of cellular cholesterol biosynthesis by increased expression of CYP51 and enhanced metabolism of lanosterol. Genetic deletion of PS1 or transgenic expression of PS1 mutants that cause early-onset Alzheimers disease led to accumulation of γ-secretase substrates and mistargeting of adaptor proteins that regulate endocytosis of the LDL receptor. Consistent with decreased endocytosis of these receptors, PS1 mutant mice have elevated levels of apolipoprotein E in the brain. Thus, these data demonstrate a functional link between two major genetic factors that cause early-onset and late-onset Alzheimers disease.

High‐Dose Statin Treatment Does Not Alter Plasma Marker for Brain Cholesterol Metabolism in Patients With Moderately Elevated Plasma Cholesterol Levels

Statins inhibit endogenous cholesterol synthesis, up‐regulate low‐density lipoprotein (LDL) receptor expression in mammalian liver cells, and thus decrease circulating LDL‐cholesterol concentrations. As cholesterol seems to play a role in the development of neurodegenerative diseases, it is of interest to evaluate the effect of high dosages of statins (eg, atorvastatin or simvastatin) on brain cholesterol metabolism. Plasma samples from 44 participants (aged 30–69 years, 16 men and 18 women) of an earlier randomized, placebo‐controlled, double‐blind trial, who took 40 mg atorvastatin or 80 mg simvastatin daily for 2 months, were used to analyze total cholesterol, its precursor lathosterol, and its metabolites 24(S)‐hydroxycholesterol and 27‐hydroxycholesterol. Despite a significant decrease in absolute plasma concentrations of oxysterols, total cholesterol, and its endogenous synthesis rate, indicated by a decreased ratio of lathosterol to cholesterol, the plasma 24(S)‐hydroxycholesterol to cholesterol ratio, a surrogate marker of brain cholesterol homeostasis, remained unchanged. Short‐term high‐dose atorvastatin and simvastatin treatment does not seem to influence brain cholesterol metabolism in patients with moderately elevated plasma cholesterol levels.

Absence of ApoE upregulates murine brain ApoD and ABCA1 levels, but does not affect brain sterol levels, while human ApoE3 and human ApoE4 upregulate brain cholesterol precursor levels

Apolipoprotein E (apoE) is a regulator of peripheral cholesterol homeostasis, and the apoE-isoform E4 is a major risk factor for the development of Alzheimers disease (AD). Accumulating evidence suggests a key role for aberrant cholesterol metabolism in AD. We hypothesized that apoE-deficiency in mice not only affects cholesterol homeostasis in the periphery, but also in the brain, and that this can be restored by astrocyte-specific expression of human apoE3, but not apoE4. Using gas-chromatography mass-spectrometry, we found that absence of apoE in mice does not affect brain cholesterol homeostasis although serum sterol levels increase dramatically, especially when the apoE-knockout mice are fed a high fat diet. We provide evidence suggesting that apoD and the ATP-binding Cassette Transporter A1 (ABCA1) play a compensatory role in the apoE-deficient brain. Surprisingly, astrocyte-specific expression of human apoE3 or apoE4 in brains of apoE-knockout mice significantly increases brain levels of cholesterol and its precursors compared to control mice, indicative of an increased cholesterol synthesis rate in the brain. This increase is independent of the apoE-isoform, suggesting that the detrimental effect of apoE4 on the pathogenesis of AD is unlikely to be due to an apoE-isoform effect on brain cholesterol homeostasis.