Possible anti-depressant effect of efavirenz and pro-depressive-like effect of voriconazole in specified doses in various experimental models of depression in mice

Unbiased insights into the multiplicity of the CYP46A1 brain effects in 5XFAD mice treated with low dose-efavirenz

Cytochrome P450 46A1 (CYP46A1) is the CNS-specific cholesterol 24-hydroxylase that controls cholesterol elimination and turnover in the brain. In mouse models, pharmacologic CYP46A1 activation with low-dose efavirenz or by gene therapy mitigates the manifestations of various brain disorders, neurologic, and nonneurologic, by affecting numerous, apparently unlinked biological processes. Accordingly, CYP46A1 is emerging as a promising therapeutic target; however, the mechanisms underlying the multiplicity of the brain CYP46A1 activity effects are currently not understood. We proposed the chain reaction hypothesis, according to which CYP46A1 is important for the three primary (unifying) processes in the brain (sterol flux through the plasma membranes, acetyl-CoA, and isoprenoid production), which in turn affect a variety of secondary processes. We already identified several processes secondary to changes in sterol flux and herein undertook a multiomics approach to compare the brain proteome, acetylproteome, and metabolome of 5XFAD mice (an Alzheimer's disease model), control and treated with low-dose efavirenz. We found that the latter had increased production of phospholipids from the corresponding lysophospholipids and a globally increased protein acetylation (including histone acetylation). Apparently, these effects were secondary to increased acetyl-CoA production. Signaling of small GTPases due to their altered abundance or abundance of their regulators could be affected as well, potentially via isoprenoid biosynthesis. In addition, the omics data related differentially abundant molecules to other biological processes either reported previously or new. Thus, we obtained unbiased mechanistic insights and identified potential players mediating the multiplicity of the CYP46A1 brain effects and further detailed our chain reaction hypothesis.

7,8-Dihydroxy Efavirenz Is Not as Effective in CYP46A1 Activation In Vivo as Efavirenz or Its 8,14-Dihydroxy Metabolite

High dose (S)-efavirenz (EFV) inhibits the HIV reverse transcriptase enzyme and is used to lower HIV load. Low-dose EFV allosterically activates CYP46A1, the key enzyme for cholesterol elimination from the brain, and is investigated as a potential treatment for Alzheimer's disease. Simultaneously, we evaluate EFV dihydroxymetabolites for in vivo brain effects to compare with those of (S)-EFV. We have already tested (rac)-8,14dihydroxy EFV on 5XFAD mice, a model of Alzheimer's disease. Herein, we treated 5XFAD mice with (rac)-7,8dihydroxy EFV. In both sexes, the treatment modestly activated CYP46A1 in the brain and increased brain content of acetyl-CoA and acetylcholine. Male mice also showed a decrease in the brain levels of insoluble amyloid β40 peptides. However, the treatment had no effect on animal performance in different memory tasks. Thus, the overall brain effects of (rac)-7,8dihydroxy EFV were weaker than those of EFV and (rac)-8,14dihydroxy EFV and did not lead to cognitive improvements as were seen in treatments with EFV and (rac)-8,14dihydroxy EFV. An in vitro study assessing CYP46A1 activation in co-incubations with EFV and (rac)-7,8dihydroxy EFV or (rac)-8,14dihydroxy EFV was carried out and provided insight into the compound doses and ratios that could be used for in vivo co-treatments with EFV and its dihydroxymetabolite.

The Diagnostic Use of the Plasma Quantification of 24S-Hydroxycholesterol and Other Oxysterols in Neurodegenerative Disease

Cholesterol regulates fluidity and structure of cellular membranes. The brain is involved in signal transduction, synaptogenesis, and membrane trafficking. An impairment of its metabolism was observed in different neurodegenerative diseases, such as Multiple Sclerosis, Alzheimer, and Huntington diseases. Because of the blood-brain barrier, cholesterol cannot be uptaken from the circulation and all the cholesterol is locally synthetized. The excess cholesterol in neurons is converted into 24S-hydroxycholesterol (24OHC) by the cholesterol 24-hydroxylase (CYP46A1). The plasmatic concentration of 24OHC results in the balance between cerebral production and liver elimination. It is related to the number of metabolically active neurons in the brain. Several factors that affect the brain cholesterol turnover and the liver elimination of oxysterols, the genetic background, nutrition, and lifestyle habits were found to significantly affect plasma levels of 24OHC. Reduced levels of 24OHC were found related to the loss of metabolically active cells and the degree of brain atrophy. The dysfunction of the blood-brain barrier, inflammation, and increased cholesterol turnover might overlap with this progressive reduction giving temporary increased levels of 24OHC.The study of plasma 24OHC is likely to offer an insight into brain cholesterol turnover with a limited diagnostic power.

The normalizing effects of the CYP46A1 activator efavirenz on retinal sterol levels and risk factors for glaucoma in Apoj-/- mice

Apolipoprotein J (APOJ) is a multifunctional protein with genetic evidence suggesting an association between APOJ polymorphisms and Alzheimer's disease as well as exfoliation glaucoma. Herein we conducted ocular characterizations of Apoj^-/- mice and found that their retinal cholesterol levels were decreased and that this genotype had several risk factors for glaucoma: increased intraocular pressure and cup-to-disk ratio and impaired retinal ganglion cell (RGC) function. The latter was not due to RGC degeneration or activation of retinal Muller cells and microglia/macrophages. There was also a decrease in retinal levels of 24-hydroxycholesterol, a suggested neuroprotectant under glaucomatous conditions and a positive allosteric modulator of N-methyl-D-aspartate receptors mediating the light-evoked response of the RGC. Therefore, Apoj^-/- mice were treated with low-dose efavirenz, an allosteric activator of CYP46A1 which converts cholesterol into 24-hydroxycholesterol. Efavirenz treatment increased retinal cholesterol and 24-hydroxycholesterol levels, normalized intraocular pressure and cup-to-disk ratio, and rescued in part RGC function. Retinal expression of Abcg1 (a cholesterol efflux transporter), Apoa1 (a constituent of lipoprotein particles), and Scarb1 (a lipoprotein particle receptor) was increased in EVF-treated Apoj^-/- mice, indicating increased retinal cholesterol transport on lipoprotein particles. Ocular characterizations of Cyp46a1^-/- mice supported the beneficial efavirenz treatment effects via CYP46A1 activation. The data obtained demonstrate an important APOJ role in retinal cholesterol homeostasis and link this apolipoprotein to the glaucoma risk factors and retinal 24-hydroxycholesterol production by CYP46A1. As the CYP46A1 activator efavirenz is an FDA-approved anti-HIV drug, our studies suggest a new therapeutic approach for treatment of glaucomatous conditions.

The potential of CYP46A1 as a novel therapeutic target for neurological disorders: An updated review of mechanisms

Cholesterol is a key component of the cell membrane that impacts the permeability, fluidity, and functions of membrane-bound proteins. It also participates in synaptogenesis, synaptic function, axonal growth, dendrite outgrowth, and microtubule stability. Cholesterol biosynthesis and metabolism are in balance in the brain. Its metabolism in the brain is mediated mainly by CYP46A1 or cholesterol 24-hydroxylase. It is responsible for eliminating about 80% of the cholesterol excess from the human brain. CYP46A1 converts cholesterol to 24S-hydroxycholesterol (24HC) that readily crosses the blood-brain barrier and reaches the liver for the final elimination process. Studies show that cholesterol and 24HC levels change during neurological diseases and conditions. So, it was hypothesized that inhibition or activation of CYP46A1 would be an effective therapeutic strategy. Accordingly, preclinical studies, using genetic and pharmacological interventions, assessed the role of CYP46A1 in main neurodegenerative disorders such as Parkinson's disease, Huntington's disease, Alzheimer's disease, multiple sclerosis, spinocerebellar ataxias, and amyotrophic lateral sclerosis. In addition, its role in seizures and brain injury was evaluated. The recent development of soticlestat, as a selective and potent CYP46A1 inhibitor, with significant anti-seizure effects in preclinical and clinical studies, suggests the importance of this target for future drug developments. Previous studies have shown that both activation and inhibition of CYP46A1 are of therapeutic value. This article, using recent studies, highlights the role of CYP46A1 in various brain diseases and insults.

Increased Acetylcholine Levels and Other Brain Effects in 5XFAD Mice after Treatment with 8,14-Dihydroxy Metabolite of Efavirenz

Efavirenz (EFV), an FDA-approved anti-HIV drug, has off-target binding to CYP46A1, the CNS enzyme which converts cholesterol to 24-hydroxycholesterol. At small doses, EFV allosterically activates CYP46A1 in mice and humans and mitigates some of the Alzheimer's disease manifestations in 5XFAD mice, an animal model. Notably, in vitro, all phase 1 EFV hydroxymetabolites activate CYP46A1 as well and bind either to the allosteric site for EFV, neurotransmitters or both. Herein, we treated 5XFAD mice with 8,14-dihydroxyEFV, the binder to the neurotransmitter allosteric site, which elicits the highest CYP46A1 activation in vitro. We found that treated animals of both sexes had activation of CYP46A1 and cholesterol turnover in the brain, decreased content of the amyloid beta 42 peptide, increased levels of acetyl-CoA and acetylcholine, and altered expression of the brain marker proteins. In addition, male mice had improved performance in the Barnes Maze test and increased expression of the acetylcholine-related genes. This work expands our knowledge of the beneficial CYP46A1 activation effects and demonstrates that 8,14-dihydroxyEFV crosses the blood-brain barrier and has therapeutic potential as a CYP46A1 activator.

Low-Dose Anti-HIV Drug Efavirenz Mitigates Retinal Vascular Lesions in a Mouse Model of Alzheimer's Disease

A small dose of the anti-HIV drug efavirenz (EFV) was previously discovered to activate CYP46A1, a cholesterol-eliminating enzyme in the brain, and mitigate some of the manifestation of Alzheimer's disease in 5XFAD mice. Herein, we investigated the retina of these animals, which were found to have genetically determined retinal vascular lesions associated with deposits within the retinal pigment epithelium and subretinal space. We established that EFV treatment activated CYP46A1 in the retina, enhanced retinal cholesterol turnover, and diminished the lesion frequency >5-fold. In addition, the treatment mitigated fluorescein leakage from the aberrant blood vessels, deposit size, activation of retinal macrophages/microglia, and focal accumulations of amyloid β plaques, unesterified cholesterol, and Oil Red O-positive lipids. Studies of retinal transcriptomics and proteomics identified biological processes enriched with differentially expressed genes and proteins. We discuss the mechanisms of the beneficial EFV effects on the retinal phenotype of 5XFAD mice. As EFV is an FDA-approved drug, and we already tested the safety of small-dose EFV in patients with Alzheimer's disease, our data support further clinical investigation of this drug in subjects with retinal vascular lesions or neovascular age-related macular degeneration.

Targeting cytochrome P450 46A1 and brain cholesterol 24-hydroxylation to treat neurodegenerative diseases

The brain cholesterol content is determined by the balance between the pathways of in situ biosynthesis and cholesterol elimination via 24-hydroxylation catalyzed by CYP46A1 (cytochrome P450 46A1). Both pathways are tightly coupled and determine the rate of brain cholesterol turnover. Evidence is accumulating that modulation of CYP46A1 activity by gene therapy or pharmacologic means could be beneficial in case neurodegenerative and other brain diseases and affect brain processes other than cholesterol biosynthesis and elimination. This minireview summarizes these other processes, most common of which include abnormal protein accumulation, memory and cognition, motor behavior, gene transcription, protein phosphorylation as well as autophagy and lysosomal processing. The unifying mechanisms, by which these processes could be affected by CYP46A targeting are also discussed.

Cholesterol Hydroxylating Cytochrome P450 46A1: From Mechanisms of Action to Clinical Applications

Cholesterol, an essential component of the brain, and its local metabolism are involved in many neurodegenerative diseases. The blood-brain barrier is impermeable to cholesterol; hence, cholesterol homeostasis in the central nervous system represents a balance between in situ biosynthesis and elimination. Cytochrome P450 46A1 (CYP46A1), a central nervous system-specific enzyme, converts cholesterol to 24-hydroxycholesterol, which can freely cross the blood-brain barrier and be degraded in the liver. By the dual action of initiating cholesterol efflux and activating the cholesterol synthesis pathway, CYP46A1 is the key enzyme that ensures brain cholesterol turnover. In humans and mouse models, CYP46A1 activity is altered in Alzheimer’s and Huntington’s diseases, spinocerebellar ataxias, glioblastoma, and autism spectrum disorders. In mouse models, modulations of CYP46A1 activity mitigate the manifestations of Alzheimer’s, Huntington’s, Nieman-Pick type C, and Machao-Joseph (spinocerebellar ataxia type 3) diseases as well as amyotrophic lateral sclerosis, epilepsy, glioblastoma, and prion infection. Animal studies revealed that the CYP46A1 activity effects are not limited to cholesterol maintenance but also involve critical cellular pathways, like gene transcription, endocytosis, misfolded protein clearance, vesicular transport, and synaptic transmission. How CYP46A1 can exert central control of such essential brain functions is a pressing question under investigation. The potential therapeutic role of CYP46A1, demonstrated in numerous models of brain disorders, is currently being evaluated in early clinical trials. This review summarizes the past 70 years of research that has led to the identification of CYP46A1 and brain cholesterol homeostasis as powerful therapeutic targets for severe pathologies of the CNS.

Brain Acetyl-CoA Production and Phosphorylation of Cytoskeletal Proteins Are Targets of CYP46A1 Activity Modulation and Altered Sterol Flux

Cholesterol and 24-hydroxycholesterol are the most abundant brain sterols and represent the substrate and product, respectively, of cytochrome P450 46A1 (CYP46A1), a CNS-specific enzyme. CYP46A1 controls cholesterol elimination and turnover in the brain, the two processes that determine the rate of brain sterol flux through the plasma membranes and thereby the properties of these membranes. Brain sterol flux is decreased in Cyp46a1-/- mice compared to wild-type mice and increased in 5XFAD mice (a model of Alzheimer's disease) when they are treated with a small dose of efavirenz, a CYP46A1 activator. Herein, we first assessed the brain proteome (synaptosomal fractions) and phospho-proteome (synaptosomal fractions and brain homogenates) of efavirenz-treated and control 5XFAD mice. Then, based on the pattern of protein abundance change, we conducted acetyl-CoA measurements (brain homogenates and mitochondria) and metabolic profiling (brain homogenates). The phospho-proteomics datasets were used for comparative analyses with the datasets obtained by us previously on mice with the same changes (efavirenz-treated and control 5XFAD mice from a different treatment paradigm) or with changes in the opposite direction (Cyp46a1-/- vs wild-type mice) in brain sterol flux. We found that CYP46A1 activity or the rate of brain sterol flux affects acetyl-CoA-related metabolic pathways as well as phosphorylation of cytoskeletal and other proteins. Knowledge of the key roles of acetyl-CoA and cytoskeletal phosphorylation in cell biology expands our understanding of the significance of CYP46A1-mediated cholesterol 24-hydroxylation in the brain and provides an additional explanation for why CYP46A1 activity modulations are beneficial in mouse models of different brain diseases.

CYP46A1-dependent and independent effects of efavirenz treatment

Cholesterol excess in the brain is mainly disposed via cholesterol 24-hydroxylation catalysed by cytochrome P450 46A1, a CNS-specific enzyme. Cytochrome P450 46A1 is emerging as a promising therapeutic target for various brain diseases with both enzyme activation and inhibition having therapeutic potential. The rate of cholesterol 24-hydroxylation determines the rate of brain cholesterol turnover and the rate of sterol flux through the plasma membranes. The latter was shown to affect membrane properties and thereby membrane proteins and membrane-dependent processes. Previously we found that treatment of 5XFAD mice, an Alzheimer's disease model, with a small dose of anti-HIV drug efavirenz allosterically activated cytochrome P450 46A1 in the brain and mitigated several disease manifestations. Herein, we generated Cyp46a1-/- 5XFAD mice and treated them, along with 5XFAD animals, with efavirenz to ascertain cytochrome P450 46A1-dependent and independent drug effects. Efavirenz-treated versus control Cyp46a1-/- 5XFAD and 5XFAD mice were compared for the brain sterol and steroid hormone content, amyloid β burden, protein and mRNA expression as well as synaptic ultrastructure. We found that the cytochrome P450 46A1-dependent efavirenz effects included changes in the levels of brain sterols, steroid hormones, and such proteins as glial fibrillary acidic protein, Iba1, Munc13-1, post-synaptic density-95, gephyrin, synaptophysin and synapsin-1. Changes in the expression of genes involved in neuroprotection, neurogenesis, synaptic function, inflammation, oxidative stress and apoptosis were also cytochrome P450 46A1-dependent. The total amyloid β load was the same in all groups of animals, except lack of cytochrome P450 46A1 decreased the production of the amyloid β40 species independent of treatment. In contrast, altered transcription of genes from cholinergic, monoaminergic, and peptidergic neurotransmission, steroid sulfation and production as well as vitamin D3 activation was the main CYP46A1-independent efavirenz effect. Collectively, the data obtained reveal that CYP46A1 controls cholesterol availability for the production of steroid hormones in the brain and the levels of biologically active neurosteroids. In addition, cytochrome P450 46A1 activity also seems to affect the levels of post-synaptic density-95, the main postsynaptic density protein, possibly by altering the calcium/calmodulin-dependent protein kinase II inhibitor 1 expression and activity of glycogen synthase kinase 3β. Even at a small dose, efavirenz likely acts as a transcriptional regulator, yet this regulation may not necessarily lead to functional effects. This study further confirmed that cytochrome P450 46A1 is a key enzyme for cholesterol homeostasis in the brain and that the therapeutic efavirenz effects on 5XFAD mice are likely realized via cytochrome P450 46A1 activation.

Brain sterol flux mediated by cytochrome P450 46A1 affects membrane properties and membrane-dependent processes

Cytochrome P450 46A1 encoded by CYP46A1 catalyzes cholesterol 24-hydroxylation and is a CNS-specific enzyme that controls cholesterol removal and turnover in the brain. Accumulating data suggest that increases in cytochrome P450 46A1 activity in mouse models of common neurodegenerative diseases affect various, apparently unlinked biological processes and pathways. Yet, the underlying reason for these multiple enzyme activity effects is currently unknown. Herein, we tested the hypothesis that cytochrome P450 46A1-mediated sterol flux alters physico-chemical properties of the plasma membranes and thereby membrane-dependent events. We used 9-month old 5XFAD mice (an Alzheimer's disease model) treated for 6 months with the anti-HIV drug efavirenz. These animals have previously been shown to have improved behavioral performance, increased cytochrome P450 46A1 activity in the brain, and increased sterol flux through the plasma membranes. We further examined 9-month old Cyp46a1 ^-/- mice, which have previously been observed to have cognitive deficits and decreased sterol flux through brain membranes. Synaptosomal fractions from the brain of efavirenz-treated 5XFAD mice had essentially unchanged cholesterol levels as compared to control 5XFAD mice. However with efavirenz treatment in these mice, there were changes in the membrane properties (increased cholesterol accessibility, ordering, osmotic resistance, and thickness) as well as total glutamate content and ability to release glutamate in response to mild stimulation. Similarly, the cholesterol content in synaptosomal fractions from the brain of Cyp46a1 ^-/- mice was essentially the same as in wild type mice but knockout of Cyp46a1 was associated with changes in membrane properties and glutamate content and its exocytotic release. Changes in Cyp46a1 ^-/- mice were in the opposite direction to those observed in efavirenz-treated vs control 5XFAD mice. Incubation of synaptosomal fractions with the inhibitors of glycogen synthase kinase 3, cyclin-dependent kinase 5, protein phosphatase 1/2A or calcineurin, and protein phosphatase 2B revealed that increased sterol flux in efavirenz-treated vs control 5XFAD mice affected the ability of all four enzymes to modulate glutamate release. In contrast, in Cyp46a1 ^-/- vs wild type mice, decreased sterol flux altered the ability of only cyclin-dependent kinase 5 and protein phosphatase 2B to regulate the glutamate release. Collectively, our results support cytochrome P450 46A1-mediated sterol flux as an important contributor to the fundamental properties of the membranes, protein phosphorylation, and synaptic transmission Also, our data provide an explanation of how one enzyme, cytochrome P450 46A1, can affect multiple pathways and processes and serve as a common potential target for several neurodegenerative disorders.

Cholesterol 24-Hydroxylation by CYP46A1: Benefits of Modulation for Brain Diseases

Cholesterol 24-hydroxylation is the major mechanism for cholesterol removal from the brain and the reaction catalyzed by cytochrome P450 46A1 (CYP46A1), a CNS-specific enzyme. This review describes CYP46A1 in the context of cholesterol homeostasis in the brain and summarizes available experimental data on CYP46A1 association with different neurologic diseases, including the mechanisms by which changes in the CYP46A1 activity in the brain could be beneficial for these diseases. The modulation of CYP46A1 activity by genetic and pharmacologic means is also presented along with a brief synopsis of the two clinical trials that evaluate CYP46A1 as a therapeutic target for Alzheimer's disease as well as Dravet and Lennox-Gastaut syndromes.