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.