CYP46A1 activation by low-dose efavirenz enhances brain cholesterol metabolism in subjects with early Alzheimer's disease

Alan J Lerner, Steven E Arnold, Erin Maxfield, Aaron Koenig, Maria E Toth, Brooke Fortin, Natalia Mast, Bianca A Trombetta, John Denker, Andrew A Pieper, Curtis Tatsuoka, Sangeetha Raghupathy, Irina A Pikuleva, Alan J Lerner, Steven E Arnold, Erin Maxfield, Aaron Koenig, Maria E Toth, Brooke Fortin, Natalia Mast, Bianca A Trombetta, John Denker, Andrew A Pieper, Curtis Tatsuoka, Sangeetha Raghupathy, Irina A Pikuleva

Abstract

Background: Efavirenz is an anti-HIV drug, and cytochrome P450 46A1 (CYP46A1) is a CNS-specific enzyme that metabolizes cholesterol to 24-hydroxycholesterol (24HC). We have previously shown that allosteric CYP46A1 activation by low-dose efavirenz in a transgenic mouse model of Alzheimer's disease (AD) enhanced both cholesterol elimination and turnover in the brain and improved animal performance in memory tests. Here, we sought to determine whether CYP46A1 could be similarly activated by a low-dose efavirenz in human subjects. METHODS: This pilot study enrolled 5 subjects with early AD. Participants were randomized to placebo (n = 1) or two daily efavirenz doses (50 mg and 200 mg, n = 2 for each) for 20 weeks and evaluated for safety and CYP46A1 target engagement (plasma 24HC levels). A longitudinal mixed model was used to ascertain the statistical significance of target engagement. We also measured 24HC in CSF and conducted a unique stable isotope labeling kinetics (SILK) study with deuterated water to directly measure CYP46A1 activity changes in the brain.

Results: In subjects receiving efavirenz, there was a statistically significant within-group increase (P ≤ 0.001) in the levels of plasma 24HC from baseline. The levels of 24HC in the CSF of subjects on the 200-mg dose of efavirenz were also increased. Target engagement was further supported by the labeling kinetics of 24HC by deuterated water in the SILK study. There were no serious adverse effects in any subjects.

Conclusions: Our findings suggest efavirenz target engagement in human subjects with early AD. This supports the pursuit of a larger trial for further determination and confirmation of the efavirenz dose that exerts maximal enzyme activation, as well as evaluation of this drug's effects on AD biomarkers and clinical symptomatology.

Trial registration: ClinicalTrials.gov, NCT03706885.

Keywords: 24-Hydroxycholesterol; Alzheimer’s disease; CYP46A1; Efavirenz; Stable isotope labeling kinetics.

Conflict of interest statement

The authors declare that they have no competing interests.

© 2022. The Author(s).

Figures

Fig. 1
Fig. 1
A summary of major study measures in trial participants. 24HC, 24-hydroxycholesterol; Baseline, baseline visit; Chol, cholesterol; Aβ40 and Aβ42, amyloid β peptides 40 and 42; pTau, phosphorylated tau; tTau, total tau; MoCA, the Montreal Cognitive Assessment; week 8, week 20, and week 22 in-clinic visits
Fig. 2
Fig. 2
A summary of the SILK experiment. This experiment was conducted in one subject (501–110) on a daily 200-mg EFV dose. A Ion abundance at m/z corresponding to the incorporation of one (504), two (505), and three (506) 2H into plasma 24-hydroxycholesterol (24HC). The peak at m/z 503 represents the sterol molecular ion. The data for week 0 show the background natural abundance of the 24HC mass isotopomers. B Plasma 24HC and body water (inset) enrichment with 2H. The dashed line indicates the areas under the curve (AUC), which were used for the estimation of the EFV effect on CYP46A1 activity. W, week of the clinic visit. EFV treatment stopped at W 20

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