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Reduction of Plasma 24S-Hydroxycholesterol (Cerebrosterol) Levels Using High-Dosage Simvastatin in Patients With Hypercholesterolemia
Evidence That Simvastatin Affects Cholesterol Metabolism in the Human Brain
Sandra Locatelli, PhD;
Dieter Lütjohann, PhD;
Hartmut H.-J. Schmidt, MD;
Carsten Otto, MD;
Ulrike Beisiegel, PhD;
Klaus von Bergmann, MD
Arch Neurol. 2002;59:213-216.
ABSTRACT
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Background Previous studies have shown that patients with early onset of Alzheimer
disease and vascular dementia have higher levels of circulating brain-derived
24S-hydroxycholesterol (cerebrosterol).Two recent epidemiological studies
indicated that treatment with inhibitors of cholesterol synthesis (statins)
reduces the incidence of Alzheimer disease.
Objective To test the hypothesis that treatment with high-dosage simvastatin reduces
circulating levels of 24S-hydroxycholesterol.
Design Prospective, 24-week treatment trial for lowering of cholesterol levels.
We conducted assessments at baseline, week 6, and week 24.
Setting An academic outpatient clinical study.
Patients Eighteen patients who met the criteria for hypercholesterolemia.
Intervention Treatment with 80 mg/d of simvastatin at night.
Main Outcome Measures Plasma lipoprotein levels were measured enzymatically; lathosterol,
by means of gas chromatography; and 24S-hydroxycholesterol, by means of gas
chromatography–mass spectrometry.
Results Simvastatin reduced total plasma cholesterol levels by 36% and 35% after
6 and 24 weeks, respectively (P<.001). Lathosterol
levels were reduced by 74% and 72%, respectively, and the ratio of lathosterol
to cholesterol, an indicator of whole-body cholesterol synthesis, was reduced
by 60% and 61%, respectively (P<.001). Plasma
24S-hydroxycholesterol levels were lowered by 45% and 53%, respectively (P<.001). The ratio of 24S-hydroxycholesterol to cholesterol
also decreased significantly (-12% [P= .01]
and -23% [P<.002], respectively). The further
reduction of 24S-hydroxycholesterol levels and its ratio to cholesterol from
weeks 6 to 24 was also significant (P= .02 for both).
Conclusions The greater reduction of plasma concentrations of 24S-hydroxycholesterol
compared with cholesterol indicates that simvastatin in a dosage of 80 mg/d
reduces cholesterol turnover in the brain. The present results might describe
a possible mechanism of how long-term treatment with statins could reduce
the incidence of Alzheimer disease.
INTRODUCTION
ELEVATED PLASMA concentrations of cholesterol have been implicated as
a possible risk factor for Alzheimer disease (AD).1-5
Results of in vitro studies suggest that cholesterol favors the formation
of ß-amyloid in the brain.6-11
Accumulation of ß-amyloid in specific brain regions of patients with
AD is thought to cause neurodegeneration.10, 12
Incubation of amyloid precursor protein-transfected human embryonic cells
with lovastatin, a 3ß-hydroxy-3ß-methylglutaryl–coenzyme A
reductase inhibitor (statin), reduces intracellular cholesterol levels and ß-amyloid
production.9-10,13
Two recent epidemiological studies provided evidence of a lower prevalence
of diagnosed AD and vascular dementia (VD) in patients with hypercholesterolemia
who are taking statins.14-15 However,
the studies do not indicate that the lower occurrence of AD and VD during
treatment with statins is due to their reduction of plasma cholesterol levels,
decreased cholesterol synthesis in the central nervous system, or other mechanisms.
Two recent studies16-17 demonstrated
that patients with early-onset AD and VD have higher plasma concentrations
of 24S-hydroxycholesterol than do subjects without neurologic diseases or
patients with depression. In humans, 24S-hydroxycholesterol is almost exclusively
produced in the brain and is important for cerebral cholesterol homeostasis.18-20 A continuous flux
of this oxysterol across the blood-brain barrier is found.18-19
The higher concentrations of plasma 24S-hydroxycholesterol in patients with
early-onset AD and VD could be the result of increased cerebral cholesterol
turnover due to cellular degradation, altered intracellular cholesterol metabolism,
increased enzyme activity, or increased cholesterol synthesis in specific
brain areas.
The aim of the present study was to investigate whether simvastatin,
a potent statin for lowering of cholesterol levels that probably passes the
blood-brain barrier in the same way as lovastatin, also reduces plasma concentrations
of 24S-hydroxycholesterol.21 Therefore, we
studied the influence of high-dosage simvastatin (80 mg/d) on lipid levels
and circulating plasma concentrations of 24S-hydroxycholesterol in patients
with hypercholesterolemia.
PATIENTS AND METHODS
PATIENTS
Outpatients with primary hypercholesterolemia were enrolled in 4 centers
for the study. The study was in accordance with the Helsinki Declaration,
and approvals were obtained by all local ethical committees. Written informed
consent was obtained from all patients after the nature of the procedure had
been fully explained. Inclusion criteria for enrollment in the study were
as follows: age between 21 and 70 years, low-density lipoprotein (LDL) cholesterol
level of at least 160 mg/dL (4.1 mmol/L), and triglyceride level of no greater
than 350 mg/dL (4.0 mmol/L). None of the patients had had impaired renal or
liver function, diabetes mellitus, thyroid dysfunction, acute coronary heart
disease, myocardial infarction, or coronary bypass surgery within the previous
3 months, and none had received drug therapy for lowering of lipid levels
during the past 6 weeks.
STUDY DESIGN AND INTERVENTIONS
Eighteen patients (12 men and 6 women; mean [SD] age, 50 ± 12
years; mean [SD] body mass index [calculated as weight in kilograms divided
by the square of height in meters], 26 ± 3) were enrolled in this prospective
study. After a 4-week placebo run-in period with a diet low in cholesterol
intake (<300 mg/d), patients were treated with 80 mg/d of simvastatin at
night for 24 weeks. Fasting blood samples for the analysis of plasma lipoprotein
levels were obtained after an overnight fast after the 4-week placebo run-in
period and after 24 weeks of treatment. Samples for determination of plasma
cholesterol, lathosterol, and 24S-hydroxycholesterol levels were obtained
at the end of the 4-week placebo run-in period and after 6 and 24 weeks of
treatment. Total cholesterol and triglyceride levels were determined enzymatically
using commercially available kits (Boehringer Mannheim, Mannheim, Germany).
High-density lipoprotein (HDL) cholesterol level was determined enzymatically
after precipitation of apolipoprotein B–containing particles with phosphotungstic
acid; LDL cholesterol level was calculated using the formula of Friedewald
et al22; and lathosterol level was quantified
by means of gas-liquid chromatography and flame-ionization detection using
5 -cholestane as an internal standard.23
Level of 24S-hydroxycholesterol was analyzed by means of an isotope dilution
method using gas chromatography–mass spectrometry.16
The variability of the measurements of lathosterol and 24S-hydroxycholesterol
levels was assessed by means of 6-fold workup of a single serum sample. The
coefficient of variation for lathosterol was 6.3% (mean [SD], 0.063 ±
0.004 mg/dL; n = 6); for 24S-hydroxycholesterol, 5.9% (mean [SD], 68 ±
4 ng/mL; n = 6).
STATISTICAL ANALYSIS
We used Wilcoxon matched-pair signed rank test to compare differences
at baseline and after 6 and/or 24 weeks of treatment. P values of lower than .05 were considered significant.
RESULTS
Treatment with 80 mg/d of simvastatin resulted in the expected changes
in plasma lipoprotein concentrations. Total cholesterol level was lowered
after 6 and 24 weeks by 36% and 35%, respectively (Table 1). Thus, maximal reduction of total plasma cholesterol level
was obtained after 6 weeks of treatment. Levels of LDL cholesterol and triglycerides
were reduced significantly after 24 weeks by 43% (P<.001)
and 30% (P = .006), respectively, whereas HDL cholesterol
level increased by 8% (P = .02). Lathosterol level
was lowered by 74% and 72% (P<.001) after 6 and
24 weeks, respectively. In addition, reduction of the ratio of lathosterol
to cholesterol did not differ after 6 (60%) and 24 weeks (61%) of simvastatin
administration (Table 1).
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Levels of Serum Lipids, Lathosterol, and 24S-Hydroxycholesterol, and
Their Ratio to Cholesterol Before and During Treatment With Simvastatin*
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Administration of simvastatin reduced the plasma concentrations of 24S-hydroxycholesterol
in all patients after 6 weeks of treatment on average from 114 to 63 ng/mL
(Table 1). A further reduction
was observed after 24 weeks (-8%; P = .02),
although the additional lowering was only observed in 12 of the 18 patients.
Individual plasma concentrations of 24S-hydroxycholesterol before and during
the treatment period are given in Figure 1. In 1 patient, a marked increase in 24S-hydroxycholesterol level
could not be attributed to a change in drug treatment, because the concentrations
of lathosterol and cholesterol remained unchanged, indicating good compliance.
A new measurement was not possible because of the lack of additional plasma
samples. The ratio of 24S-hydroxycholesterol to cholesterol was also significantly
reduced after 6 and 24 weeks of simvastatin treatment by 12% (P = .01) and 23% (P<.002), respectively
(Figure 2). The additional reduction
from week 6 to week 24 was also significant (P =
.02).
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Figure 1. Plasma concentration of 24S-hydroxycholesterol
at baseline (week 0) and after 6 and 24 weeks of treatment with simvastatin
(80 mg/d) in 18 patients with hypercholesterolemia.
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Figure 2. The ratio of 24S-hydroxycholesterol
to cholesterol in plasma at baseline (week 0) and after 6 and 24 weeks of
treatment with simvastatin (80 mg/d) in 18 patients with hypercholesterolemia.
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COMMENT
The results of the present study show for the first time that simvastatin
apparently affects cholesterol metabolism in the human brain. Simvastatin,
given in a dosage of 80 mg/d at night, reduces plasma 24S-hydroxycholesterol
level, which is synthesized in the central nervous system.18, 20, 24-25
Furthermore, the percentage of reduction after 6 and 24 weeks of treatment
occurred independent of the reduction in total cholesterol or lathosterol
concentrations, indicating a different place of action. The reduction of total
and LDL cholesterol levels during the present study supports the effect of
simvastatin on plasma lipoprotein concentrations as described in a previous
study with an identical dosage of simvastatin.26
Plasma cholesterol level is lowered as a result of the inhibition of cholesterol
synthesis in the liver and subsequent increased expression of LDL receptors,
which result in an up-regulated catabolic rate for plasma LDL. The decreased
cholesterol synthesis was confirmed by the reduction of the ratio of lathosterol
to cholesterol, an indicator of hepatic27 and
total cholesterol synthesis.28 During treatment
with simvastatin, the lowering effect on plasma 24S-hydroxycholesterol level
was significantly more pronounced than that on plasma cholesterol level, suggesting
that high-dosage simvastatin also affects cholesterol metabolism in the brain.
Indeed, administration of simvastatin to guinea pigs diminishes de novo cholesterol
synthesis in the brain, followed by reduced concentrations of ß-amyloid,
without altering total cholesterol content.29
Maintaining the high-dosage simvastatin treatment for a total of 24 weeks
did not lead to a more pronounced decrease in the plasma concentrations of
total cholesterol or lathosterol or the ratio of lathosterol to cholesterol.
In contrast, 24S-hydroxycholesterol level was additionally reduced by 12%
during the following 18 weeks, and the ratio of 24S-hydroxycholesterol to
cholesterol, by 8%. Whether long-term treatment with lower dosages of simvastatin
or other statins also reduces 24S-hydroxycholesterol levels remains to be
elucidated.
Previous studies16-17 have
shown that lower plasma concentrations of 24S-hydroxycholesterol in severely
affected patients with AD is a peripheral marker for loss of cholesterol and/or
cholesterol 24S-hydroxylase in the brain. Thus, early detection of predicted
candidates for AD (early-onset AD) by means of elevated levels of plasma 24S-hydroxycholesterol
or its ratio to cholesterol should initiate a protective measure to prove
the beneficial therapy using statins for prevention of AD and VD.
Although the reduction of plasma cholesterol level may be responsible
for the lower incidence of AD, the recent results from Jick et al15 suggest that only statins, and no other drug that
lowers lipid levels, exhibit this preventive effect. Thus, the results of
the present study might provide the pharmacological basis for a possible mechanism
of action of statins in preventing AD and VD. However, only prospective randomized
studies can prove our hypothesis that the reduction in plasma 24S-hydroxycholesterol
concentrations by means of statins, indicating impaired cholesterol metabolism
in the brain, is a method for preventing AD and/or VD.
AUTHOR INFORMATION
Accepted for publication September 18, 2001.
Author contributions: Study concept and design (Drs Locatelli, Lütjohann, Schmidt, Otto, Beisiegel, and
von Bergmann); acquisition of data (Drs Locatelli,
Lütjohann, and von Bergmann); analysis and interpretation of data (Drs Locatelli, Lütjohann, and von Bergmann); drafting of
the manuscript (Drs Locatelli, Lütjohann, and von Bergmann); critical
revision of the manuscript for important intellectual content (Drs Locatelli, Lütjohann, and von Bergmann); statistical expertise (Drs Locatelli, Lütjohann, and von Bergmann); obtaining
funding (Drs Locatelli, Lütjohann, and von Bergmann); administrative, technical, or material support (Drs Otto, Schmidt, and Beisiegel).
The study was supported by an unrestricted grant from MSD Sharp &
Dohme GmbH, München, Germany, and by grant 01EC9402 from the Bundesministerium
für Bildung, Forschung, Wissenschaft und Technologie, Bonn, Germany.
We thank staff technicians Heike Pranke and Anja Kerksiek for their
skillful assistance.
Corresponding author and reprints: Klaus von Bergmann, MD, Department
of Clinical Pharmacology, Universitätsklinikum, University of Bonn, Sigmund-Freud-Strasse
25, D-53105 Bonn, Germany (e-mail: vonbergmann{at}uni-bonn.de).
From the Department of Clinical Pharmacology, University of Bonn, Bonn
(Drs Locatelli, Lütjohann, and von Bergmann), the Medical Department,
Charité, Berlin (Dr Schmidt), the Medical Department II, Klinikum University
of Munich, Großhadern, Munich (Dr Otto), and Medical Clinic, University
Hospital Hamburg, Hamburg (Dr Beisiegel), Germany.
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