The Relationship Between CYP46A1 Polymorphism and Suicide Risk: A Preliminary Investigation

Suicide is a global public health issue, with a particularly high incidence in individuals suffering from Major Depressive Disorder (MDD). The role of cholesterol in suicide risk remains controversial, prompting investigations into genetic markers that may be implicated. This study examines the association between CYP46A1 polymorphisms, specifically SNPs rs754203 and rs4900442, and suicide risk in a Mexican MDD patient cohort. Our study involved 188 unrelated suicide death victims, 126 MDD patients, and 144 non-suicidal controls. Genotypic and allelic frequencies were assessed using the Real Time-polymerase chain reaction method, and associations with suicide risk were evaluated using chi-square tests. The study revealed significant differences in allelic and genotypic frequencies in rs754203 SNP between suicide death and controls. The CYP46A1 rs754203 genotype G/G was significantly linked with suicide, and the G allele was associated with a higher risk of suicide (OR = 1.370, 95% CI = 1.002-1.873). However, we did not observe any significant differences in genotype distribution or allele frequencies of CYP46A1 rs4900442. Our study suggests that carriers of the CYP46A1 rs754203 G allele (A/G + G/G) may play a role in suicidal behavior, especially in males. Our findings support that the CYP46A1 gene may be involved in susceptibility to suicide, which has not been investigated previously. These results underscore the importance of further research in different populations to elucidate the genetic underpinnings of the role of CYP46A1 in suicide risk and to develop targeted interventions for at-risk populations.

Investigation of the absolute bioavailability, mass balance, metabolism, and excretion of the cholesterol 24-hydroxylase inhibitor soticlestat in healthy volunteers

AIMS

Our aim was to determine the absolute bioavailability, mass balance, metabolism and excretion of soticlestat (TAK-935).

METHODS

An open-label, two-period, single-site, phase 1 study was conducted in six healthy men. In Period 1, a single 300 mg dose of soticlestat was administered orally, followed by a 15-min intravenous infusion of [14 C]soticlestat 50 μg (~1 μCi) 10 min later. In Period 2, a single 300 mg dose (~100 μCi) of [14 C]soticlestat in solution was administered orally. Samples were collected, analysed for radioactivity or unchanged soticlestat, and profiled for metabolites.

RESULTS

In Period 1, soticlestat had an absolute bioavailability of 12.6% (90% confidence interval, 7.81-20.23%). In Period 2, there was near-complete recovery of total radioactivity (TRA) following a 300 mg dose of [14 C]soticlestat: urine, 94.8% (standard deviation [SD], 1.35%); faeces, 2.7% (SD, 1.67%). Of TRA, 0.1% (SD, 0.09%) and 0.6% (SD, 0.21%) were recovered as soticlestat and metabolite M-I in urine, respectively. In plasma, soticlestat and M-I reached geometric mean maximum observed concentrations of 1352 ng/mL (geometric percent coefficient of variation [gCV%], 61.3) and 253.2 ng/mL (gCV%, 44.1) after 25 min and declined with mean terminal half-lives (SD) of 5.7 (2.90) and 2.0 (0.15) h, respectively. Soticlestat represented 4.9% of TRA in plasma. Soticlestat was rapidly eliminated primarily via O-glucuronidation to metabolite M3, which was the dominant species in plasma (92.6%) and urine (86%).

CONCLUSIONS

This study indicates that soticlestat and its metabolites are rapidly cleared and eliminated, lowering the risk of dose accumulation from repeated dosing and supporting further investigation of soticlestat.

CYP46A1-mediated cholesterol turnover induces sex-specific changes in cognition and counteracts memory loss in ovariectomized mice

The brain-specific enzyme CYP46A1 controls cholesterol turnover by converting cholesterol into 24S-hydroxycholesterol (24OH). Dysregulation of brain cholesterol turnover and reduced CYP46A1 levels are observed in Alzheimer's disease (AD). In this study, we report that CYP46A1 overexpression in aged female mice leads to enhanced estrogen signaling in the hippocampus and improved cognitive functions. In contrast, age-matched CYP46A1 overexpressing males show anxiety-like behavior, worsened memory, and elevated levels of 5α-dihydrotestosterone in the hippocampus. We report that, in neurons, 24OH contributes to these divergent effects by activating sex hormone signaling, including estrogen receptors. CYP46A1 overexpression in female mice protects from memory impairments induced by ovariectomy while having no effects in gonadectomized males. Last, we measured cerebrospinal fluid levels of 24OH in a clinical cohort of patients with AD and found that 24OH negatively correlates with neurodegeneration markers only in women. We suggest that CYP46A1 activation is a valuable pharmacological target for enhancing estrogen signaling in women at risk of developing neurodegenerative diseases.

24S-Hydroxycholesterol in Neuropsychiatric Diseases: Schizophrenia, Autism Spectrum Disorder, and Bipolar Disorder

Neuropsychiatric diseases (NPDs) are severe, debilitating psychiatric conditions that affect the nervous system. These are among the most challenging disorders in medicine. Some examples include Alzheimer's, anxiety disorders, autism spectrum disorder, bipolar disorder, and schizophrenia. NPDs represent an ever-increasing burden on public health and are prevalent throughout the world. For most of these diseases, the particular etiopathogeneses are still enigmatic. NPDs are also associated with structural and functional changes in the brain, along with altered neurotransmitter and neuroendocrine systems.Approximately 25% of the total human body cholesterol is located in the brain. Its involvement in neuronal functions starts in the early growth stages and remains important throughout adulthood. It is also an integral part of the neuronal membrane, ensuring membrane lipid organization and regulating membrane fluidity. The main mechanism for removing cholesterol from the brain is cholesterol 24-hydroxylation by cytochrome P450 46A1 (CYP46A1), an enzyme specifically found in the central nervous system. Although research on 24S-OHC and its role in neuropsychiatric diseases is still in its early stages, this oxidized cholesterol metabolite is thought to play a crucial role in the etiology of NPDs. 24S-OHC can affect neurons, astrocytes, oligodendrocytes, and vascular cells. In addition to regulating the homeostasis of cholesterol in the brain, this oxysterol is involved in neurotransmission, oxidative stress, and inflammation. The role of 24S-OHC in NPDs has been found to be controversial in terms of the findings so far. There are several intriguing discrepancies in the data gathered so far regarding 24S-OHC and NPDs. In fact, 24S-OHC levels were reported to have decreased in a number of NPDs and increased in others.Hence, in this chapter, we first summarize the available data regarding 24S-OHC as a biomarker in NPDs, including schizophrenia, autism spectrum disorder, and bipolar disorder. Then, we present a brief synopsis of the pharmacological targeting of 24S-OHC levels through the modulation of CYP46A1 activity.

Clinical Characterization of [18F]T-008, a Cholesterol 24-Hydroxylase PET Ligand: Dosimetry, Kinetic Modeling, Variability, and Soticlestat Occupancy

This series of studies characterized [18F]T-008, a PET radiotracer for imaging cholesterol 24-hydroxylase (CH24H), in healthy volunteers (ClinicalTrials.gov identifier NCT02497235). Assessments included radiation dosimetry, kinetic modeling, test-retest variability (TRT) evaluation, and a dose occupancy evaluation using soticlestat, a selective CH24H inhibitor. Soticlestat is currently in phase 3 development for the treatment of seizures in Dravet syndrome and Lennox-Gastaut syndrome. Methods: In the dosimetry study, 5 participants (3 men) underwent serial whole-body scans to estimate organ-absorbed doses and effective doses of [18F]T-008 using OLINDA/EXM 1.1. For the kinetic modeling and TRT study, 6 participants (all men) underwent two 210-min dynamic [18F]T-008 PET scans with arterial blood sampling. The regional total volume of distribution was estimated using a 1-tissue-compartment model, a 2-tissue-compartment model, and Logan graphic analysis. In the dose occupancy study, 11 participants (all men) underwent 120-min scans at baseline and 2 time points (peak and trough) after receiving single oral doses of soticlestat (50-600 mg). The relationship between effect-site soticlestat concentration and brain occupancy was evaluated with a specially developed pharmacokinetic model and a saturable maximal occupancy model. Results: The estimated mean whole-body effective dose was 0.0292 mSv/MBq (SD, 0.00147 mSv/MBq). [18F]T-008 entered the brain rapidly, with a distribution consistent with known CH24H distribution densities. The 2-tissue-compartment model and Logan graphic analysis best described the tracer kinetics. The mean TRT for estimating total volume of distribution was 7%-15%. Single doses of soticlestat in the range 50-600 mg resulted in occupancies of 64%-96% at 2 h and 11%-79% at 24 h. The estimated half-maximal effect-site concentration of soticlestat was 5.52 ng/mL. Conclusion: [18F]T-008 is a suitable PET radiotracer for quantitatively analyzing CH24H in the human brain. Using [18F]T-008 and PET, we demonstrated that soticlestat was brain-penetrant and established target engagement by displacing [18F]T-008 in a dose-dependent manner in the brain.

Cytochrome P450 Family 46 Subfamily A Member 1 Promotes the Progression of Colorectal Cancer by Inducing Tumor Cell Proliferation and Angiogenesis

BACKGROUND/AIM

Cytochrome P450 family 46 subfamily A member 1 (CYP46A1) has been implicated in the development and progression of various cancers. This study aimed to analyze the expression of CYP46A1, examining its relationship with oncogenic behaviors, and determining its prognostic implications in colorectal cancer (CRC).

MATERIALS AND METHODS

A total of 225 patients with CRC who underwent curative surgical resection were examined using paraffin-embedded tissue blocks and subjected to tumor-specific survival analysis. The expression of CYP46A1 was assessed in CRC tissues through reverse transcription-polymerase chain reaction, western blotting, and immunohistochemistry. The CRC cells' apoptosis, proliferation, angiogenesis, and lymphangiogenesis were analyzed using terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assays, alongside immunohistochemical staining for Ki-67, CD34, and D2-40 antibodies.

RESULTS

CYP46A1 expression was found to be up-regulated in CRC tissues compared to normal colorectal mucosa. Such expression was significantly associated with advanced stage, deeper tumor invasion, lymph node metastasis, distant metastasis, and decreased survival. Furthermore, the mean Ki-67 labeling index and microvessel density values in CYP46A1-positive tumors were significantly elevated compared to CYP46A1-negative tumors. However, there was no discernible correlation between CYP46A1 expression and either the apoptotic index or lymphatic vessel density value.

CONCLUSION

CYP46A1 promotes CRC progression, specifically through the induction of tumor cell proliferation and angiogenesis. The insights provided may hold potential implications for future therapeutic interventions targeting CYP46A1.

Phytosterols reverse antiretroviral-induced hearing loss, with potential implications for cochlear aging

Cholesterol contributes to neuronal membrane integrity, supports membrane protein clustering and function, and facilitates proper signal transduction. Extensive evidence has shown that cholesterol imbalances in the central nervous system occur in aging and in the development of neurodegenerative diseases. In this work, we characterize cholesterol homeostasis in the inner ear of young and aged mice as a new unexplored possibility for the prevention and treatment of hearing loss. Our results show that cholesterol levels in the inner ear are reduced during aging, an effect that is associated with an increased expression of the cholesterol 24-hydroxylase (CYP46A1), the main enzyme responsible for cholesterol turnover in the brain. In addition, we show that pharmacological activation of CYP46A1 with the antiretroviral drug efavirenz reduces the cholesterol content in outer hair cells (OHCs), leading to a decrease in prestin immunolabeling and resulting in an increase in the distortion product otoacoustic emissions (DPOAEs) thresholds. Moreover, dietary supplementation with phytosterols, plant sterols with structure and function similar to cholesterol, was able to rescue the effect of efavirenz administration on the auditory function. Altogether, our findings point towards the importance of cholesterol homeostasis in the inner ear as an innovative therapeutic strategy in preventing and/or delaying hearing loss.

Investigation of Potential Drug Targets for Cholesterol Regulation to Treat Alzheimer's Disease

Despite extensive research and seven approved drugs, the complex interplay of genes, proteins, and pathways in Alzheimer's disease remains a challenge. This implies the intricacies of the mechanism for Alzheimer's disease, which involves the interaction of hundreds of genes, proteins, and pathways. While the major hallmarks of Alzheimer's disease are the accumulation of amyloid plaques and tau protein tangles, excessive accumulation of cholesterol is reportedly correlated with Alzheimer's disease patients. In this work, protein-protein interaction analysis was conducted based upon the genes from a clinical database to identify the top protein targets with most data-indicated involvement in Alzheimer's disease, which include ABCA1, CYP46A1, BACE1, TREM2, GSK3B, and SREBP2. The reactions and pathways associated with these genes were thoroughly studied for their roles in regulating brain cholesterol biosynthesis, amyloid beta accumulation, and tau protein tangle formation. Existing clinical trials for each protein target were also investigated. The research indicated that the inhibition of SREBP2, BACE1, or GSK3B is beneficial to reduce cholesterol and amyloid beta accumulation, while the activation of ABCA1, CYP46A1, or TREM2 has similar effects. In this study, Sterol Regulatory Element-Binding Protein 2 (SREBP2) emerged as the primary protein target. SREBP2 serves a pivotal role in maintaining cholesterol balance, acting as a transcription factor that controls the expression of several enzymes pivotal for cholesterol biosynthesis. Novel studies suggest that SREBP2 performs a multifaceted role in Alzheimer's disease. The hyperactivity of SREBP2 may lead to heightened cholesterol biosynthesis, which suggested association with the pathogenesis of Alzheimer's disease. Lowering SREBP2 levels in an Alzheimer's disease mouse model results in reduced production of amyloid-beta, a major contributor to Alzheimer's disease progression. Moreover, its thoroughly analyzed crystal structure allows for computer-aided screening of potential inhibitors; SREBP2 is thus selected as a prospective drug target. While more protein targets can be added onto the list in the future, this work provides an overview of key proteins involved in the regulation of brain cholesterol biosynthesis that may be further investigated for Alzheimer's disease intervention.

Adipokine pathways are altered in hippocampus of an experimental mouse model of Alzheimer's disease

A growing body of evidence suggests that β-amyloid peptides (Aβ) are unlikely to be the only factor involved in Alzheimer's disease (AD) aetiology. In fact, a strong correlation has been established between AD patients and patients with type 2 diabetes and/or cholesterol metabolism alterations. In addition, a link between adipose tissue metabolism, leptin signalling in particular, and AD has also been demonstrated. In the present study we analyzed the expression of molecules related to metabolism, with the main focus on leptin and prolactin signalling pathways in an APPswe/PS1dE9 (APP/PS1) transgenic mice model, at 3 and 6 months of age, compared to wild-type controls. We have chosen to study 3 months-old APP/PS1 animals at an age when neither the cognitive deficits nor significant Aβ plaques in the brain are present, and to compare them to the 6 months-old mice, which exhibit elevated levels of Aβ in the hippocampus and memory loss. A significant reduction in both mRNA and protein levels of the prolactin receptor (PRL-R) was detected in the hippocampi of 3 months old APP/PS1 mice, with a decrease in the levels of the leptin receptor (OB-R) first becoming evident at 6 months of age. We proceeded to study the expression of the intracellular signalling molecules downstream of these receptors, including stat (1-5), sos1, kras and socs (1-3). Our data suggest a downregulation in some of these molecules such as stat-5b and socs (1-3), in 3 months-old APP/PS1 brains. Likewise, at the same age, we detected a significant reduction in mRNA levels of lrp1 and cyp46a1, both of which are involved in cholesterol homeostasis. Taken together, these results demonstrate a significative impairment in adipokine receptors signalling and cholesterol regulation pathways in the hippocampus of APP/PS1 mice at an early age, prior to the Aβ plaque formation.

Is it possible to improve memory function by upregulation of the cholesterol 24S-hydroxylase (CYP46A1) in the brain?

We previously described a heterozygous mouse model overexpressing human HA-tagged 24S-hydroxylase (CYP46A1) utilizing a ubiquitous expression vector. In this study, we generated homozygotes of these mice with circulating levels of 24OH 30–60% higher than the heterozygotes. Female homozygous CYP46A1 transgenic mice, aged 15 months, showed an improvement in spatial memory in the Morris water maze test as compared to the wild type mice. The levels of N-Methyl-D-Aspartate receptor 1, phosphorylated-N-Methyl-D-Aspartate receptor 2A, postsynaptic density 95, synapsin-1 and synapthophysin were significantly increased in the hippocampus of the CYP46A1 transgenic mice as compared to the controls. The levels of lanosterol in the brain of the CYP46A1 transgenic mice were significantly increased, consistent with a higher synthesis of cholesterol. Our results are discussed in relation to the hypothesis that the flux in the mevalonate pathway in the brain is of importance in cognitive functions.

Steady-state levels of retinal 24S-hydroxycholesterol are maintained by glial cells intervention after elevation of intraocular pressure in the rat

PURPOSE

Our previous studies suggested that CYP46A1 and 24S-hydroxycholesterol (24SOH) may be associated with glaucoma. Loss of CYP46A1-expressing retinal ganglion cells is involved in the activation of glia, and therefore possibly in the disbalance of cholesterol. In this context, the purpose of our present work was to emphasize the glial and longitudinal CYP46A1 expression after an interventional glaucoma-related stress triggered by elevated intraocular pressure (IOP).

METHODS

Sprague-Dawley rats were submitted to laser photocoagulation of the trabecular meshwork, limbus and episcleral veins in one eye to induce elevated IOP. Rats were euthanized at days 3, 14, 30 and 60 (n = 10 per time-point), and 24SOH was measured in plasma and retina by gas chromatography-mass spectrometry. CYP46A1 was quantified by Western blotting. Glial activation was assessed by glial fibrillary acidic protein immunoreactivity in Western blots and retinal cryosections.

RESULTS

Sustained high IOP was observed in experimental eyes from day 1 to day 21. Plasma MCP-1 and ICAM-1, quantified using multiplex assay kits, were increased at day 3. Glial activation was observed bilaterally at all time-points, at lower levels in contralateral eyes than in experimental eyes. In experimental retinas, CYP46A1 expression showed a transient increase at day 3 and then returned to baseline. Plasma and retinal 24SOH peaked at day 14 and 30, respectively.

CONCLUSIONS

These data show that CYP46A1 expression was induced early in response to retinal stress but remained constant at late time-points, reinforcing the constitutive role of CYP46A1 in maintaining cholesterol balance in neuronal tissues.

A pilot study of gene/gene and gene/environment interactions in Alzheimer disease

BACKGROUND

Although some genes associated with increased risk of Alzheimer Disease (AD) have been identified, few data exist related to gene/gene and gene/environment risk of AD. The purpose of this pilot study was to explore gene/gene and gene/environment associations in AD and to obtain data for sample size estimates for larger, more definitive studies of AD.

METHODS

The effect of gene/gene and gene/environment interaction related to late onset Alzheimer Disease (LOAD) was investigated in 153 subjects with LOAD and 302 gender matched controls enrolled in the Personalized Medicine Research Project, a population-based bio-repository. Genetic risk factors examined included APOE, ACE, OLR1,and CYP46 genes, and environmental factors included smoking, total cholesterol, LDL, HDL, triglycerides, C-reactive protein, blood pressure, statin use, and body mass index.

RESULTS

The mean age of the cases was 78.2 years and the mean age of the controls was 87.2 years. APOE4 was significantly associated with LOAD (OR=3.55, 95%CL=1.70, 7.45). Cases were significantly more likely to have ever smoked cigarettes during their life (49.3% versus 38.4%, p=0.03). The highest recorded blood pressure and pulse pressure measurements were significantly higher in the controls than the cases (all P<0.005). Although not statistically significant in this pilot study, the relationship of the following factors was associated in opposite directions with LOAD based on the presence of an APOE4 allele: obesity at the age of 50, ACE, OLR1, and CYP46.

CONCLUSIONS

These pilot data suggest that gene/gene and gene/environment interactions may be important in LOAD, with APOE, a known risk factor for LOAD, affecting the relationship of ACE and OLR1 to LOAD. Replication with a larger sample size and in other racial/ethnic groups is warranted and the allele and risk factor frequencies will assist in choosing an appropriate sample size for a definitive study.

Structural basis of drug binding to CYP46A1, an enzyme that controls cholesterol turnover in the brain

Cytochrome P450 46A1 (CYP46A1) initiates the major pathway of cholesterol elimination from the brain and thereby controls cholesterol turnover in this organ. We determined x-ray crystal structures of CYP46A1 in complex with four structurally distinct pharmaceuticals; antidepressant tranylcypromine (2.15 Å), anticonvulsant thioperamide (1.65 Å), antifungal voriconazole (2.35 Å), and antifungal clotrimazole (2.50 Å). All four drugs are nitrogen-containing compounds that have nanomolar affinity for CYP46A1 in vitro yet differ in size, shape, hydrophobicity, and type of the nitrogen ligand. Structures of the co-complexes demonstrate that each drug binds in a single orientation to the active site with tranylcypromine, thioperamide, and voriconazole coordinating the heme iron via their nitrogen atoms and clotrimazole being at a 4 Å distance from the heme iron. We show here that clotrimazole is also a substrate for CYP46A1. High affinity for CYP46A1 is determined by a set of specific interactions, some of which were further investigated by solution studies using structural analogs of the drugs and the T306A CYP46A1 mutant. Collectively, our results reveal how diverse inhibitors can be accommodated in the CYP46A1 active site and provide an explanation for the observed differences in the drug-induced spectral response. Co-complexes with tranylcypromine, thioperamide, and voriconazole represent the first structural characterization of the drug binding to a P450 enzyme.

Cholesterol-24S-hydroxylase (CYP46A1) is specifically expressed in neurons of the neural retina

Increasing biological findings argue for the importance of cholesterol-24S-hydroxylase (CYP46A1) in cholesterol homeostasis in cerebral structures. Based on the similarity between the brain and the neural retina, the aim of the current study was to evaluate the expression of CYP46A1 in the mammalian retina. RT-PCR analysis of CYP46A1 in bovine samples revealed the highest expression in the neural retina. The retinal pigment epithelium expressed CYP46A1 gene at a low level while the ciliary body showed no expression. Immunohistochemical evaluation of the posterior pole of rat retina showed that the protein is specifically expressed in neurons, whereas cone-rods photoreceptors were negative for CYP46A1 staining. The metabolite produced by CYP46A1, 24S-hydroxycholesterol, was almost exclusively found in neural retina, the concentration therein being more than 10-fold higher than in the retinal pigment epithelium or the ciliary body. The results of the current study are consistent with our primary hypothesis: the neural retina specifically expresses cholesterol-24S-hydroxylase, a metabolizing enzyme responsible for the removal of cholesterol in neurons. Based on the link between cholesterol-24S-hydroxylase, 24S-hydroxycholesterol, and neurologic disorders, CYP46A1 may be a valuable gene candidate for retinal pathologies like age-related macular degeneration or glaucomas, and 24S-hydroxycholesterol may be involved in the onset of the degenerative processes in these diseases.

24S-hydroxycholesterol in relation to disease manifestations of acute experimental autoimmune encephalomyelitis

Levels of the brain-specific cholesterol metabolite 24S-hydroxycholesterol are proposed as possible biomarkers for multiple sclerosis (MS). It is not yet clear for which aspect of the MS disease manifestations 24S-hydroxycholesterol is a reflection. We studied the relation of serum levels of 24S-hydroxycholesterol and other sterols to the disease characteristics of acute experimental autoimmune encephalomyelitis (EAE), an animal model for MS. Serum was analyzed for cholesterol precursors, oxysterols, and plant sterols during the course of disease development. Significantly increased levels of the cholesterol metabolites 24S-hydroxycholesterol and 27-hydroxycholesterol were observed on day 9, before the onset of clinical signs. The serum levels of these oxysterols gradually increased up to 193% and 415%, respectively, at day 17, when clinical symptoms had recovered. Total cholesterol levels were slightly but significantly decreased on day 9 and day 17 in treated animals. Serum levels of cholesterol precursors and plant sterols decreased gradually from day 11 and day 14, respectively. Immunostaining of the 24S-hydroxycholesterol-forming enzyme Cyp46 was shown in macrophage infiltrates. In vitro experiments confirmed the presence of Cyp46 in macrophages and showed a decreased expression after LPS treatment. The data indicate that changes in serum oxysterols occur early in EAE and can be formed by macrophages. These early changes indicate an important role for oxysterols in the development of EAE.

Plasma 24S Hydroxycholesterol Response to Statins in Alzheimer’s Disease Patients: Effects of Gender, CYP46, and ApoE Polymorphisms

A number of epidemiologic studies suggest an association between plasma total cholesterol and risk for Alzheimer's disease (AD). Additionally, it has been suggested that treatment with statins, drugs that block cholesterol biosynthesis, lower the incidence and prevalence of AD and of vascular dementia. This review provides an overview of cholesterol transport within the central nervous system and the impact of statins on brain cholesterol metabolism in subjects with AD. Brain cholesterol is converted to 24-S-hydroxycholesterol, a reaction catalyzed by CYP46. The oxysterol traverses the blood-brain barrier and is transported to the liver by plasma lipoproteins. The levels of 24-S-hydroxy-cholesterol are a reflection of brain cholesterol turnover. Subjects with AD reportedly have high levels of the oxysterol possibly reflecting neuronal death with release of cell membrane cholesterol. We show gender dimorphism in plasma levels of 24-S-hydroxycholesterol in subjects with AD and significant reductions in plasma levels of the oxysterol during treatment with standard doses of statins (lovastatin, simvastatin, and pravastatin). Polymorphisms of apolipoprotein E and CYP46 do not influence the effect of statins on plasma levels of 24-S-hydroxycholesterol. There were no untoward effects of the standard doses of statin for the duration of treatment. Statins are currently in trial to determine their effect on the course of AD.

Oxysterols: functional significance in fetal development and the maintenance of normal retinal function

PURPOSE OF REVIEW

Recent findings extend the biologic activities of oxysterols as ligands for nuclear receptors to a role in morphogenesis during fetal development and to a role in the metabolism of photooxidation products of cholesterol in the retina.

RECENT FINDINGS

A 1000-fold increase of the 27-hydroxy metabolite of 7-dehydrocholesterol in the plasma of children with Smith-Lemli-Opitz syndrome imply that intermediates in cholesterol synthesis follow alternate pathways of metabolism that generate novel oxysterols. A mouse model also finds an increase in sterol intermediates as the proximate cause of dysmorphisms. A role for oxysterols in the effects of Sonic hedgehog protein focuses on their role in normal fetal development. Both CYP27A1 and CYP46A1 are expressed in primate retina indicating that local metabolism of 7-ketocholesterol to nontoxic derivatives is important for preventing retinal degeneration.

SUMMARY

Recent data expand the functional roles of oxysterols to fetal development and to the detoxification of oxidation products of cholesterol. This review shifts the focus of attention from studies of their ligand-binding activity to studies of animal models that indicate a number of important biologic effects during fetal development and during the aging process.

[Correlation of cholesterol 24-hydroxylase and ATP-binding cassette transporter A1 polymorphisms with Alzheimer's disease]

OBJECTIVE

To investigate the association of the single nucleotide polymorphisms (SNPs) A-->G in the intron 2 of cholesterol 24-hydroxylase (CYP46) gene and G-->A (R219K) in the exon 6 of ATP-binding cassette transporter A1 (ABCA1) gene with sporadic Alzheimer's disease (SAD) in the Han Chinese population.

METHODS

Peripheral blood samples were collected from 168 SAD patients, 74 males and 94 females, aged 74 +/- 8 (52 - 95), with an average age at onset of 69 +/- 7 (47 - 86), and sex-, and age-matched 215 healthy persons. PCR-restriction fragment length polymorphism (PCR-RFLP) was used to detect the genotypes. Apolipoprotein E (ApoE) genotyping was conducted. The strength of association between the polymorphisms and AD was estimate.

RESULTS

The frequency of ApoE genotype of the SAD patients was 14%, significantly higher than that of the controls (5.1%, chi(2) = 19.060, P < 0.01). The risk of SAD in those with at least one epsilon 4 allele was 2.8 times that in those without epsilon 4 allele (OR = 2.82, 95% CI = 1.54 - 5.17, P = 0.001). There was no significant difference in the genotype or allele frequencies for CYP46 gene between the SAD patients and controls. However, there was an obvious association between the polymorphism of ABCA1 gene and SAD (chi(2) = 8.230, P = 0.016). The frequency of G/A + A/A genotypes in the SAD patients was 61.3%, significantly lower than that of the controls (73.5%, chi(2) = 6.444, P = 0.011). The risk of SAD in the carriers of A alleles (G/A + A/A genotypes) was significantly lower than those with GG genotype by 43% (adjusted OR = 0.57, 95% CI = 0.36 - 0.91, P = 0.019), and the risk of SAD in the AA homozygote carriers was significantly lower than that of the GG genotype carriers by 60% (adjusted OR = 0.40; 95% CI = 0.21 - 0.77, P = 0.006).

CONCLUSION

The CYP46 intron 2 polymorphism may not be associated with the risk of AD, but AA genotype or A allele of ABCA1 gene may have a protective effect for AD in Han Chinese.

Intron 2 (T/C) CYP46 polymorphism is associated with Alzheimer's disease in Chinese patients

BACKGROUND

Cholesterol metabolism has been implicated in the pathophysiology of Alzheimer's disease (AD), and cholesterol-related genes are plausible candidate genes for AD. Genetic association of CYP46A1 polymorphisms with AD had been under extensive investigations; however, observations on intron 2 T-->C (rs754203) generated inconclusive results.

OBJECTIVE

To analyse an independent data set in a Chinese population to see whether the polymorphic site rs754203 of the CYP46A1 gene is associated with AD.

METHODS

We analysed 130 sporadic AD patients and 110 healthy controls of the Southern Chinese origin.

RESULTS

An association between the genotype frequency and AD was suggested in the general population (p = 0.047, odds ratio, OR = 1. 61, 95% confidence interval, CI = 0.96-2.70), while the association was most significant in the apolipoprotein E (ApoE) epsilon4-negative group (p = 0.004, OR = 2.54, 95% CI =1.31-4.95). Linkage disequilibrium block prediction results also favoured this association. Consistent with previous reports, intron 3 C-->T (rs4900442) polymorphism did not show any evidence of association; in our data set ApoEepsilon4 was confirmed to be a genetic risk factor for AD (p = 0.0016, OR = 2.76, 95% CI = 1.50-5.11).

Polymorphisms of cholesterol metabolism genes CYP46 and ABCA1 and the risk of sporadic Alzheimer's disease in Chinese

Recent studies have demonstrated that cholesterol metabolism might play an important role in Alzheimer's disease (AD). Cholesterol 24-hydroxylase (CYP46) and ATP-binding cassette transporter A1 (ABCA1) have both been proposed to be involved in cholesterol metabolism in the brain. The purpose of this case-control study was to determine whether single nucleotide polymorphisms (SNPs) A-->G in the intron 2 of CYP46 gene and G-->A (R219K) in the exon 7 of ABCA1 gene are associated with sporadic AD in the Chinese Han population. Genotypes were determined by PCR-restriction fragment length polymorphism (PCR-RFLP) in 168 sporadic AD patients and 215 controls. There was no significant difference in the genotype or allele frequencies for CYP46 gene between AD patients and controls. However, we found an obvious association between the polymorphism of ABCA1 gene and AD (chi(2)=8.230, P=0.016). The risk for AD was significantly decreased in K allele (RK+KK genotypes) (adjusted OR=0.57, 95% CI=0.36-0.91, P=0.019) or KK homozygote carriers (adjusted OR=0.40; 95% CI=0.21-0.77, P=0.006) compared with RR genotypes carriers. Our results do not support a genetic association between the intron 2 polymorphism of CYP46 gene and the risk of sporadic AD, but reveal that KK genotype or K allele of ABCA1 gene may have a protective effect for sporadic AD in Chinese.

Crossing the barrier: oxysterols as cholesterol transporters and metabolic modulators in the brain

A normal brain function requires constant levels of cholesterol, and the need for constancy seems to be higher here than in any other organ. Nature has met this need by isolation of brain cholesterol by a highly efficient blood-brain barrier. As a low synthesis of cholesterol is present in the brain, a mechanism for compensatory elimination is required. A decade ago we made the unexpected finding that the favoured mechanism for this involves conversion into 24S-hydroxycholesterol, followed by diffusion over the blood-brain barrier. Recent studies by us and others on this new pathway have given new insights into the mechanisms by which cholesterol homeostasis is maintained in the brain. We recently demonstrated a flux of another oxygenated product of cholesterol, 27-hydroxycholesterol, in the opposite direction. The latter flux may be important for neurodegeneration, and may be the link between hypercholesterolaemia and Alzheimer's disease. An overview of the above studies is presented and the possibility that the cholesterol 24S-hydroxylase in the brain may be important for memory and learning and that it may be a new drug target is discussed.

Cholesterol metabolism in the brain: importance of 24S-hydroxylation

During the last three to four decades there has been an increasing interest in the interaction of circulating and brain cholesterol. Recent in vivo and in vitro studies have furthered our knowledge of cholesterol metabolism in the central nervous system (CNS). As the CNS matures and cholesterol pools in the brain become constant, the rate of de novo synthesis of cholesterol in the brain markedly declines. Besides some excretion of apoE-bound cholesterol via the CSF, another quantitatively more important mechanism has been described - the conversion of cholesterol into 24S-hydroxycholesterol, that is, in contrast to cholesterol, able to traverse the blood-brain barrier (BBB). The enzyme (CYP46a1) mediating this conversion has been characterized at the molecular level and is mainly located in neurons. Like other oxysterols, 24S-hydroxycholesterol is efficiently converted into normal bile acids or excreted in bile in its sulfated and glucuronidated form. Within the last 10 years the interest in studying the mechanisms of this and other cholesterol transport systems has increased and the results from these in vivo and in vitro investigations are reviewed.

Lovastatin Modulates Increased Cholesterol and Oxysterol Levels and Has a Neuroprotective Effect on Rat Hippocampal Neurons After Kainate Injury

This study was carried out to elucidate the effect of a brain-permeable statin (lovastatin) on cholesterol and oxysterol levels of the hippocampus after neuronal injury induced by the excitotoxin, kainic acid. Increased immunolabeling to cholesterol and the oxysterol biosynthetic enzyme, cholesterol 24-hydroxylase, was observed in the rat hippocampus after kainate lesions. This was accompanied by increased levels of cholesterol, 24-hydroxycholesterol (product of cholesterol 24-hydroxylase enzymatic activity), and 7-ketocholesterol in homogenates of the degenerating hippocampus as detected by gas chromatography/mass spectrometry. Hippocampi from rats or organotypic slices that had been treated with kainate plus lovastatin showed significantly lower levels of cholesterol, 24-hydroxycholesterol, and 7-ketocholesterol compared with those that had been treated with kainate only. Lovastatin also modulated hippocampal neuronal loss after kainate treatment in vivo and in vitro. The level of 24-hydroxycholesterol detected in vivo after kainate treatment (>50 microM) was found to be neurotoxic in hippocampal slice cultures. These results suggest that brain-permeable statins such as lovastatin could have a neuroprotective effect by limiting the levels of oxysterol in brain areas undergoing neurodegeneration.

Polymorphism in the cholesterol 24S-hydroxylase gene (CYP46A1) associated with the APOEpsilon3 allele increases the risk of Alzheimer's disease and of mild cognitive impairment progressing to Alzheimer's disease

BACKGROUND

Late-onset Alzheimer's disease (LOAD) is associated with changes in certain proteins, such as ApoE and Cyp46A1, of the elimination route for cerebral cholesterol. The main lipoprotein involved in its transport is ApoE whose Epsilon4 allele is the least efficient. However, the presence or absence of this allele does not determine the development of LOAD, which implies the existence of other susceptibility factors associated with the disease, such as the CYP46A1 gene that encodes the enzyme cholesterol 24S-hydroxylase.

OBJECTIVE

To find new data to contribute to the evaluation of whether the presence of the T allele in the polymorphic site rs754203 of the CYP46A1 gene leads to a greater risk of developing mild cognitive impairment (MCI) and LOAD. Furthermore, given the link between APOE and CYP46A1, we proceeded to relate both genotypes in each of the patient groups studied.

METHODS

We studied MCI and LOAD patients and also carried out an analysis of those MCI patients who progressed from a mild cognitive deterioration to a clinically evident Alzheimer's disease during the study.

RESULTS

The frequency of the CYP46A1-T allele in the LOAD patients with APOEpsilon3 alleles is significantly higher with respect to the control group; the same occurs in the group made up of LOAD patients together with the MCI patients who progressed to LOAD. The risk of developing LOAD when this allelic combination exists is 2.262 times higher (95% CI 1.337-4.202). However, having the CYP46A1-T allele does not increase the risk of suffering from LOAD in carriers of the APOEpsilon4 allele, probably because the transport of cholesterol is already affected in such patients and possibly masks the effect of the CYP46A1-T allele.

CONCLUSIONS

The CYP46A1-T allele increases the risk of suffering from LOAD in persons carrying the APOEpsilon3 allele.

Lack of association between the CYP46 gene polymorphism and Italian late-onset sporadic Alzheimer's disease

Recent studies have provided evidence toward the possible involvement of brain cholesterol homeostasis in late-onset Alzheimer's disease (LOAD). We analyzed an intronic T-->C substitution (rs 754203) of the cholesterol 24S-hydroxylase (CYP46) gene, encoding an enzyme acting on brain cholesterol turnover, which has been recently associated with an increased risk of AD, dependent or not on Apolipoprotein E (ApoE) genotype. No significant association was found for the CYP46 polymorphism in LOAD compared to the controls, even after stratification for the presence/absence of the ApoE*4 allele. Our data do not support a role of the CYP46 polymorphism as a possible susceptibility factor for developing AD.

Lipids and the pathogenesis of Alzheimer's disease: is there a link?

Alzheimer's disease (AD) is a heterogeneous neurodegenerative disorder characterized pathologically by amyloid-beta plaques, neurofibrillary tangles and neuronal loss. Its fundamental cause(s) and the pathological cascades leading to clinical symptoms remain unknown. Lipids and lipid peroxidation products have important roles in the homeostasis of the central nervous system. As well, lipid transport genes and vascular changes associated with peripheral dyslipidemia have been associated with an increased risk of AD. The present review discusses ways in which lipids may be involved in the pathogenesis of AD-associated neurodegeneration through their roles as neuronal structural components, cell modulators, or second messengers. Given the many possibilities through which lipids may be directly involved in or contribute to the pathogenesis of AD, the use of lipids as biomarkers for disease progression is discussed, as are other avenues for future research.

Brain cholesterol turnover required for geranylgeraniol production and learning in mice

The mevalonate pathway produces cholesterol and nonsterol isoprenoids, such as geranylgeraniol. In the brain, a fraction of cholesterol is metabolized in neurons by the enzyme cholesterol 24-hydroxylase, and this depletion activates the mevalonate pathway. Brains from mice lacking 24-hydroxylase excrete cholesterol more slowly, and the tissue compensates by suppressing the mevalonate pathway. Here we report that this suppression causes a defect in learning. 24-Hydroxylase knockout mice exhibit severe deficiencies in spatial, associative, and motor learning, and in hippocampal long-term potentiation (LTP). Acute treatment of wild-type hippocampal slices with an inhibitor of the mevalonate pathway (a statin) also impairs LTP. The effects of statin treatment and genetic elimination of 24-hydroxylase on LTP are reversed by a 20-min treatment with geranylgeraniol but not by cholesterol. We conclude that cholesterol turnover in brain activates the mevalonate pathway and that a constant production of geranylgeraniol in a small subset of neurons is required for LTP and learning.

Polymorphisms of the cholesterol 24-hydroxylase (CYP46A1) gene and the risk of Alzheimer's disease in a Chinese population

BACKGROUND

An increasing number of studies have suggested a link between cholesterol metabolism and Alzheimer's disease (AD), which may be mediated by its effect on amyloid processing. Intracranial cholesterol is primarily eliminated into the bloodstream through conversion into 24-hydroxycholesterol by the enzyme cholesterol 24-hydroxylase (encoded by the CYP46A1 gene). CYP46A1 is an essential gene modulating cholesterol metabolism in the brain.

METHOD

To investigate whether polymorphisms in the CYP46A1 gene modulate the risk of AD, we studied four common polymorphisms (IVS1-192, IVS2-150, IVS3-128 and IVS4-122) in 182 Chinese AD patients and 179 age-matched healthy Chinese subjects.

RESULTS AND CONCLUSION

We found that the IVS3-128 polymorphism was associated with the risk of AD (p < 0.05). Subjects homozygous for the C alleles were protected from AD with an adjusted odds ratio (OR) of 1.53 [95% confidence interval (95% CI) 0.98-2.37, p = 0.047]. However, another minor allele, IVS1-192 C, was more prevalent in the AD group and was associated with an increased risk. Haplotype analysis revealed that two of the eight common haplotypes formed by the four polymorphisms were rarely found in the AD group, suggesting a protective effect of these two haplotypes (GTCA and CCTA). The results supported the involvement of the CYP46A1 gene and cholesterol metabolism in the pathogenesis of AD.

CHOLESTEROL-METABOLIZING CYTOCHROMES P450

By catalyzing the first steps in different pathways of cholesterol degradation, cytochromes P450 (P450s) 7A1, 27A1, 11A1, and 46A1 play key roles in cholesterol homeostasis. CYP7A1 is a microsomal liver-specific enzyme that converts cholesterol to 7alpha-hydroxycholesterol. CYP27A1 is a ubiquitously expressed mitochondrial P450 that metabolizes cholesterol to 27-hydroxycholesterol. CYP11A1 also resides in mitochondria but is expressed mainly in steroidogenic tissues, where it catalyzes the conversion of cholesterol to pregnenolone. Finally, CYP46A1 is a brain-selective microsomal monooxygenase producing 24S-hydroxycholesterol from cholesterol. Catalytic efficiencies of cholesterol-metabolizing P450s vary significantly and probably reflect physiological requirements of different organs for the rate of cholesterol turnover. P450s 7A1, 27A1, 11A1, and 46A1 represent a unique system for elucidation of how different enzymes have adapted to fit their specific roles in cholesterol elimination. Studies of cholesterol-metabolizing P450s suggest that their activities could be modulated post-translationally and that they should also be considered as targets for regulation of cholesterol homeostasis.

Studies on the transcriptional regulation of cholesterol 24-hydroxylase (CYP46A1): marked insensitivity toward different regulatory axes

Mammalian CNS contains a disproportionally large and remarkably stable pool of cholesterol. Despite an efficient recycling there is some requirement for elimination of brain cholesterol. Conversion of cholesterol into 24S-hydroxycholesterol by the cholesterol 24-hydroxylase (CYP46A1) is the quantitatively most important mechanism. Based on the protein expression and plasma levels of 24S-hydroxycholesterol, CYP46A1 activity appears to be highly stable in adults. Here we have made a structural and functional characterization of the promoter of the human CYP46A1 gene. No canonical TATA or CAAT boxes were found in the promoter region. Moreover this region had a high GC content, a feature often found in genes considered to have a largely housekeeping function. A broad spectrum of regulatory axes using a variety of promoter constructs did not result in a significant transcriptional regulation. Oxidative stress caused a significant increase in transcriptional activity. The possibility of a substrate-dependent transcriptional regulation was explored in vivo in a sterol-deficient mouse model (Dhcr24 null) in which almost all cholesterol had been replaced with desmosterol, which is not a substrate for CYP46A1. Compared with heterozygous littermates there was no statistically significant difference in the mRNA levels of Cyp46a1. During the first 2 weeks of life in the wild-type mouse, however, a significant increase of Cyp46a1 mRNA levels was found, in parallel with an increase in 24S-hydroxycholesterol level and a reduction of cholesterol synthesis. The failure to demonstrate a significant transcriptional regulation under most conditions is discussed in relation to the turnover of brain and neuronal cholesterol.

Association studies of cholesterol metabolism genes (CH25H, ABCA1 and CH24H) in Alzheimer's disease

Recent studies have demonstrated that cholesterol metabolism has an important role in Alzheimer's disease (AD) pathogenesis, suggesting that cholesterol-related genes may be significant genetic risk factors for AD. Based on the results of genome-wide screens, along with biological studies, we selected three genes as candidates for AD risk factors: ATP-binding cassette transporter A1 (ABCA1), cholesterol 25-hydroxylase (CH25H) and cholesterol 24-hydroxylase (CH24H). Case-control of North American Caucasians and AD families of Caribbean Hispanic origin were examined. Although excellent biological candidates, the case-control dataset did not support the hypothesis that these three genes were associated with susceptibility to AD. Similarly, no association was found in the Caribbean Hispanic families for CH25H. However, we did observe a possible interaction between ABCA1 and APOE in the Hispanics.

[Cholesterol and Alzheimer's disease]

Epidemiological, biochemical and pharmacological investigations provide increasing number of evidences that altered cholesterol metabolism contributes to the development of Alzheimer's disease. The objective of the present paper is to review existing information about the links of cholesterol and amyloid metabolism from the clinical and proposed etiological viewpoints of the most frequent dementing disorder in Hungary. Beta-amyloid peptide, the major component of the senile plaques in the Alzheimer's disease brains is the end product of the abnormal post-translational processing of its precursor, called amyloid precursor protein. The compartmentation of the amyloid precursor protein molecule within the cell membrane is regulated by the cholesterol content of the bilayers. The amyloid precursor protein molecule could be present either in-, or outside of the membrane rafts. Any kind of process, which alters the compartmentation preference of the amyloid precursor protein molecule, by transferring it to the membrane rafts, favours beta- and gamma-secretase cleavage, and should be recognised as an amyloidogenic process. If the blood-brain barrier is intact, the brain is not able to take up the lipoprotein particles responsible for the transport of cholesterol. Instead of the active uptake, neurons and glial cells synthetize cholesterol de novo, in a process, where the rate limiting enzyme is 3-hydroxy-3-methylglutaryl coenzyme A. On the other hand, the brain specific CYP46A1 enzyme is responsible for the degradation of cholesterol into a water soluble metabolite, called 24S-OH cholesterol. The decreased CYP46A1 activity in the brain of Alzheimer's disease patients raises membrane cholesterol levels, and as a consequence the amyloid precursor protein is shifted and deposited in the cholesterol rich lipid rafts leading to beta-amyloid peptide specific metabolism. Among the polymorphic variants of the apolipoprotein E gene, the E4 allele is considered as a major risk factor for Alzheimer's disease. The E4 allele carrier Alzheimer's disease probands have increased amyloid burden, decreased beta-amyloid peptide degradation, and less effective neuronal repair mechanisms. Even as early as age 30, patients with Niemann-Pick Type C disease show clinical and neuropathological signs of Alzheimer's disease. The point mutation of the protein responsible for the endosomal transport of cholesterol is considered as a major cause of the beta-amyloid peptide deposition in the brain of Niemann-Pick Type C patients. One of the most exciting recent discovery, that Niemann-Pick Type C disease could be recognised as a disease model for Alzheimer's disease. New, promising cholesterol metabolism related therapeutic approaches are discussed, but it is emphasized that the clinical evidences regarding their efficacy in Alzheimer's disease are still missing.

The effects of gender and CYP46 and apo E polymorphism on 24S-hydroxycholesterol levels in Alzheimer's patients treated with statins

To examine the effect of gender and polymorphisms of CYP46 and apo E on plasma levels of 24S-hydroxycholesterol in Alzheimer's disease (AD) patients and to determine whether these factors contribute to the variability in responses to statin treatment. Fifty-three AD patients had measurement of plasma levels of 24S-hydroxycholesterol, plasma and lipoprotein cholesterol and genotyping of CYP46 and apo E. Thirty-nine of the subjects subsequently participated in a statin trial for 6 weeks, and had a repetition of the baseline measurements. Baseline levels of 24S-hydroxycholesterol were higher in women than in men. There was a positive and significant correlation of plasma oxysterol levels with levels of total plasma cholesterol (women: r = .72, P < .0001; men: r = .47, P = .02) and non-HDL cholesterol (women: r = .68, P < .0001; men: r = 0.51, P = .01) (and LDL cholesterol) but not HDL cholesterol levels. There was no association of CYP46 or apo E polymorphisms with plasma levels of 24S-hydroxycholesterol. AD subjects treated with statins had a similar percent reduction in lathosterol, 24S-hydroxycholesterol, total cholesterol and non-HDL (and LDL) cholesterol regardless of gender and polymorphisms of CYP46. Subjects with the 4/4 polymorphism had less reduction in the ratios of 24S-hydroxycholesterol-LDL cholesterol. Women with AD had higher levels of plasma 24S-hydroxycholesterol levels than men. Women also showed a very strong correlation of plasma levels of 24S-hydroxycholesterol-to-total and non-HDL cholesterol. This may suggest that the oxysterol may be an important marker of AD risk instead of total cholesterol, as suggested by others. Polymorphisms of CYP46 or apo E do not explain levels of oxysterol or non-HDL cholesterol or the responsiveness to statin treatment in this study.

CYP46 T/C Polymorphism is not Associated with Alzheimer’s Dementia in a Population from Hungary

Multiple genetic and environmental factors regulate the susceptibility to Alzheimer's disease (AD). Recently, several independent studies have reported that a locus on chromosome 14q32.1, where a gene encoding a cholesterol degrading enzyme of the brain, called 24-hydroxylase (CYP46A1) is located, has been linked with AD. The single nucleotide polymorphism (T/C) in intron 2 of CYP46 gene has been found to confer the risk for AD. The water soluble 24(S)-hydroxysterol is the product of the CYP46A1, and elevated plasma and cerebrospinal fluid hydroxysterol concentrations have been found in AD, reflecting increased brain cholesterol turnover or cellular degradation, due to the neurodegenerative process. A case-control study was performed on 125 AD and 102 age- and gender-matched control subjects (CNT) from Hungary, to test the association of CYP46 T/C and apolipoprotein E (ApoE) gene polymorphisms in AD. The frequency of the CYP46 C allele was similar (chi2=0.647, df=1, P=0.421, exact P=0.466, OR=0.845; 95% CI: 0.561-1.274) in both groups (CNT: 27%; 95% CI: 21.3-33.4; AD 30%; 95% CI: 25.0-36.3). The ApoE varepsilon4 allele was significantly over-represented (chi2=11.029, df=2, P=0.004) in the AD population (23.2%; 95% CI: 18.2-29.0) when compared with the CNT (11.3%; 95% CI: 7.4-16.6). The presence or absence of one or two CYP46C alleles together with the ApoE varepsilon4 allele did not increase the risk of AD (OR=3.492; 95% CI: 1.401-8.707; P<0.007 and OR=3.714; 95% CI: 1.549-8.908; P<0.003, respectively). Our results indicate that the intron 2 T/C polymorphism of CYP46 gene (neither alone, nor together with the varepsilon4 allele) does not increase the susceptibility to late-onset sporadic AD in the Hungarian population.

A simple and rapid method to measure cholesterol binding to P450s and other proteins

Cholesterol plays an important role in cellular function and membrane compartmentalization and is involved in the interaction with more than a dozen of different proteins. Using three cholesterol-metabolizing cytochrome P450s (P450s 7A1, 46A1, and 11A1), we have developed a rapid and simple assay for measurements of nanomolar to micromolar cholesterol affinities. In this assay, the P450 is incubated with a fixed amount of radiolabeled cholesterol and varying concentrations of cold cholesterol followed by separation of free and protein-bound cholesterol via filtration through a membrane. Free cholesterol is found in the flow-through fraction, whereas P450 binds to the membrane. The radioactivity of the membranes is then measured, and a saturation curve is generated after correction for nonspecific binding of cholesterol to the filter. The validity of the filter assay was confirmed by spectral assay, a traditional method to evaluate the interaction of the P450 enzymes with their substrates. Two types of membranes, one binding positively charged proteins and another binding negatively charged proteins, were identified. These membranes were also found to hold proteins through hydrophobic interactions. Thus, the cholesterol binding properties of a wide variety of proteins could be characterized using this filter assay.

A cluster of cholesterol-related genes confers susceptibility for Alzheimer's disease

OBJECTIVE

Polygenic diseases are related to the complex interplay of genetic variations. We evaluated whether clusters of cholesterol- and lipid-related genetic variations are associated with Alzheimer's disease.

METHOD

We analyzed 12 cholesterol-related single nucleotide polymorphisms and 48 control polymorphisms in 545 study participants (Alzheimer's disease group N = 284; control group N = 261). Diagnoses of Alzheimer's disease were made according to the NINCDS-ADRDA criteria. Multi-locus genetic association analysis was done with the set-association method. Dates of data collection were from January 2000 to December 2003.

RESULTS

We identified a cluster of polymorphisms in APOE, SOAT1, APOE 5'-untranslated region, OLR1, CYP46A1, LPL, LIPA, and APOA4 conferring significant (p = .0002) susceptibility for Alzheimer's disease. This gene cluster reached a diagnostic accuracy of 74% and correlated significantly (p = .018) with the levels of the brain cholesterol catabolite 24S-hydroxycholesterol in the cerebrospinal fluid.

CONCLUSION

Our results establish a novel approach for the identification of disease-related genetic clusters and demonstrate the need for multi-locus methods in the genetics of complex diseases.

CYP46: A risk factor for Alzheimer's disease or a coincidence?

Excess cholesterol is removed from the brain via hydroxylation mediated by cholesterol 24S-hydroxylase (CYP46). Although serum and cerebrospinal fluid (CSF) concentrations of 24S-hydroxycholesterol are altered during the progress of Alzheimer's disease, studies carried out to date in different populations on the association of CYP46 gene polymorphisms and risk of AD have been inconclusive. In this report, we analyzed CYP46 polymorphisms in 215 Polish AD cases and 173 healthy individuals. A fragment of CYP46 intron 2 was amplified by PCR reaction and sequenced. We discovered a new single nucleotide substitution in CYP46 intron 2, but found no difference in particular genotype or allele frequencies between AD patients and controls. However, the GG genotype of the known rs754203 polymorphic site might be a risk factor for AD, especially in APOE varepsilon4 carriers. Interestingly, in AD patients the rs754203 G allele was more frequent in males than in females. However, considering the extreme divergence of results obtained by different authors, a clear connection between the CYP46 gene and AD is questionable.

Cholesterol and apolipoprotein E in Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia in North America and Europe. The incidence of the disease rises dramatically with age. AD is a complex multifactorial disorder that involves numerous susceptibility genes, but the exact pathogenesis and biochemical basis of AD is not well understood Cholesterol is receiving a great deal of attention as a potentially crucial factor in the etiology of AD. Almost all cholesterol in the brain is synthesized in the brain. Cholesterol exits the brain through the blood-brain barrier (BBB) in the form of apolipoprotein E (ApoE) or by first being converted to a more polar compound, 24(S)-hydroxycholesterol, which is elevated in individuals with AD. The key event leading to AD appears to be the formation and aggregation in the brain of amyloid beta (Abeta) peptide, a proteolytically derived product of amyloid precursor protein (APP). Cholesterol has been demonstrated to modulate processing of APP to Abeta. High levels of cholesterol are associated with increased risk of AD. Patients taking cholesterol-lowering statins have a lower prevalence of AD. ApoE, which transports cholesterol throughout the brain, exhibits an isoform-specific association with AD such that the E4 isoform, by unknown mechanisms, shifts the onset curve toward an earlier age.

Genetic association of CYP46 and risk for Alzheimer's disease

An increasing number of studies suggest that cholesterol plays an important role in regulating beta-amyloid (Abeta) metabolism in Alzheimer's disease (AD). One of the most important mechanisms for the elimination of excess brain cholesterol is its conversion into the 24S-hydroxycholesterol catalyzed by cholesterol 24S-hydroxylase (CYP46). Preliminary evidence indicates that an intron 2 CYP46 T/C gene polymorphismis associated with increased brain Abeta load and higher risk of AD. A case-control study utilizing a clinically well-defined group of 321 sporadic AD patients and 315 control subjects was performed to test this association. Our results indicate that the intron 2 CYP46 C/C genotype may predispose to AD, and this association is independent of the apolipoprotein E genotype.

Lack of association of the cholesterol 24-hydroxylase (CYP46) intron 2 polymorphism with Alzheimer's disease

An association was recently reported between an increased risk of Alzheimer's disease and an intron 2 AA genotype of CYP46, the enzyme hydroxylating cholesterol to 24S-hydroxycholesterol. Moreover, CYP46 AA-carriers were found to have increased levels of amyloid-beta and tau in brain and cerebrospinal fluid. We determined the CYP46 intron 2 genotype in a cohort of 178 AD and 105 non-demented control subjects, but found no significant association with AD for any of the individual genotypes or alleles. Further, in an autopsy confirmed subset of this cohort, the proposed CYP46 risk genotype was not associated with any increase in the brain levels of amyloid-beta40, amyloid-beta42 or in the levels of amyloid plaques and neurofibrillary tangles. Despite growing evidence implicating cholesterol metabolism in AD risk and Abeta generation, our data does not support a robust genetic relationship between the CYP46 intron 2 polymorphism and AD risk or neuropathology.

Association between a T/C polymorphism in intron 2 of cholesterol 24S-hydroxylase gene and Alzheimer's disease in Chinese

A polymorphism (T/C) in intron 2 of the cholesterol 24-hydroxylase (CYP46) gene has recently been reported to be associated with the risk for late-onset Alzheimer's disease (LOAD). To investigate possible involvement of the CYP46 gene and apolipoprotein E (APOE) gene polymorphisms in the manifestation of LOAD, we analyzed 99 sporadic LOAD patients and 113 healthy controls of China. We found an obvious association between CYP46 TT genotype and LOAD (OR = 2.98, 95% CI 1.64-5.44, P < 0.001). A clear increase of the risk to develop LOAD was also observed in subjects carrying both the CYP46 TT genotype and the APOE epsilon4-allele (OR = 12.94, 95% CI 4.26-39.32, P < 0.001). Our data reveal that the polymorphism of CYP46 intron 2 is implicated in the susceptibility to LOAD and a strong synergistic interaction between CYP46 TT homozoygots and APOE epsilon4 carrier status on the risk of LOAD.

Expression of human cytochrome P450 46A1 in Escherichia coli: effects of N- and C-terminal modifications

Heterologous expression in Escherichia coli, subcellular distribution, solubility, and catalytic and substrate-binding properties of four truncated cytochromes P450 46A1 were investigated in the present study. All four lacked the N-terminal transmembrane region (residues 3-27), and, in addition, Delta 46A1H had a 4x His-tag fused to the C-terminus; H Delta 46A1 had the N-terminal 4x His-tag; H Delta 46A1 Delta had a 4x His-tag at the N-terminus and did not contain a proline-rich region at the C-terminus (residues 494-499); and Delta 46A1 Delta lacked the C-terminal proline-rich region. The truncated enzymes were expressed at 390-650 nmol/L culture levels, distributed at about a 1:1 ratio between the membrane fraction and the cytosol in low ionic strength buffer, and were predominantly monomers in detergent-free buffer. They had moderately decreased catalytic efficiencies for either cholesterol or 24S-hydroxycholesterol or both, whereas their substrate-binding constants were either unchanged or decreased 2-fold. The two forms, Delta 46A1 Delta and H Delta 46A1 Delta, both lacking the C-terminal proline-rich region seem to be good candidates for future crystallographic studies because they contain only 0.3-0.8% of high molecular weight aggregates and their catalytic efficiencies are decreased no more than 2.3-fold.

Intronic CYP46 polymorphism along with ApoE genotype in sporadic Alzheimer Disease: from risk factors to disease modulators

Increasing biological and clinical findings argue for a link between brain cholesterol turnover and Alzheimer Disease (AD), high cerebral levels of the former increasing Abeta load. Cerebral cholesterol elimination involves two mechanisms dependent on Apolipoprotein E (ApoE) and cholesterol 24-hydroxylase (CYP46). The aim of this study was to evaluate an intronic variation in CYP46 (intron 2, T --> C ) along with ApoE genotype as risk factors for AD and to establish the correlation between CYP46/ApoE polymorphism and disease progression. One-hundred and fifty-seven AD patients, who had been followed periodically through 1-year follow-up after enrollment, and 134 age- and gender-matched controls entered the study. The distribution of CYP46 genotypes was significantly different in AD compared to controls (P<0.004), being CYP*C allele higher in AD patients ( P<0.002). ApoE 4 genotype was more frequent in AD (41.4%) than in controls (15.9%, P<0.0001). The odds ratio (OR) for AD risk in CYP46*C carriers was 2.8, and in ApoE epsilon4 carriers was 4.05; the OR for having both CYP46*C and ApoE epsilon4 was 17.75, demonstrating the their synergic effect on AD risk. In AD patients, CYP46*C along with ApoE epsilon4 genotype were associated with a higher cognitive decline at 1-year follow-up (P<0.02). These findings provide direct evidence that CYP46 and ApoE polymorphisms synergically increase the risk for AD development, and influence on the rate of cognitive decline.

Exclusion of CYP46 and APOM as candidate genes for Alzheimer's disease in a French population

Alzheimer's disease (AD) is a complex, multifactorial disorder, probably resulting from an interaction between environmental and genetic factors. Increasing evidence points to a link between cholesterol turnover and AD, suggesting that genes implicated in brain cholesterol homeostasis may be potential candidate genes for AD. With this background, we tested the potential association of the CYP46, APOM and APOF genes with the risk of developing AD. CYP46 encodes the enzyme cholesterol 24-hydrolase, which plays a key role in brain cholesterol turnover, and APOF and APOM encode apolipoproteins belonging to the large lipocalin family, which also includes ApoE. In contrast to two previous reports but in accordance with one other, we were unable to detect an association between an intron 2 polymorphism of CYP46 and AD. We also searched for polymorphisms within the APOM and APOF by dHPLC. We were unable to detect any polymorphisms in the coding and exon/intron sequences of the APOF. Finally, we excluded APOM as a genetic determinant of AD in our large French case control population.

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 Alzheimer's 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.

Differential expression of cholesterol hydroxylases in Alzheimer's disease

Cholesterol is eliminated from neurons by oxidization, which generates oxysterols. Cholesterol oxidation is mediated by the enzymes cholesterol 24-hydroxylase (CYP46A1) and cholesterol 27-hydroxylase (CYP27A1). Immunocytochemical studies show that CYP46A1 and CYP27A1 are expressed in neurons and some astrocytes in the normal brain, and CYP27A1 is present in oligodendrocytes. In Alzheimer's disease (AD), CYP46A1 shows prominent expression in astrocytes and around amyloid plaques, whereas CYP27A1 expression decreases in neurons and is not apparent around amyloid plaques but increases in oligodendrocytes. Although previous studies have examined the effects of synthetic oxysterols on the processing of amyloid precursor protein (APP), the actions of the naturally occurring oxysterols have yet to be examined. To understand the role of cholesterol oxidation in AD, we compared the effects of 24(S)- and 27-hydroxycholesterol on the processing of APP and analyzed the cell-specific expression patterns of the two cholesterol hydroxylases in the human brain. Both oxysterols inhibited production of Abeta in neurons, but 24(S)-hydroxycholesterol was approximately 1000-fold more potent than 27-hydroxycholesterol. The IC(50) of 24(S)-hydroxycholesterol for inhibiting Abeta secretion was approximately 1 nm. Both oxysterols induced ABCA1 expression with IC(50) values similar to that for inhibition of A beta secretion, suggesting the involvement of liver X receptor. Oxysterols also inhibited protein kinase C activity and APP secretion following stimulation of protein kinase C. The selective expression of CYP46A1 around neuritic plaques and the potent inhibition of APP processing in neurons by 24(S)-hydroxycholesterol suggests that CYP46A1 affects the pathophysiology of AD and provides insight into how polymorphisms in the CYP46A1 gene might influence the pathophysiology of this prevalent disease.

Variants of CYP46A1 may interact with age and APOE to influence CSF Abeta42 levels in Alzheimer's disease

Recent studies have suggested that variants of CYP46A1, encoding cholesterol 24-hydroxylase (CYP46), confer risk for Alzheimer's disease (AD), a prospect substantiated by evidence of genetic association from several quantitative traits related to AD pathology, including cerebrospinal fluid (CSF) levels of the 42 amino-acid cleavage product of beta-amyloid (Abeta42) and the tau protein. In the present study, these claims have been explored by the genotyping of previously associated markers in CYP46A1 in three independent northern European case-control series encompassing 1323 individuals and including approximately 400 patients with measurements of CSF Abeta42 and phospho-tau protein levels. Tests of association in case-control models revealed limited evidence that CYP46A1 variants contributed to AD risk across these samples. However, models testing for potential effects upon CSF measures suggested a possible interaction of an intronic marker (rs754203) with age and APOE genotype. In stratified analyses, significant effects were evident that were restricted to elderly APOE epsilon4 carriers for both CSF Abeta42 ( P=0.0009) and phospho-tau ( P=0.046). Computational analyses indicate that the rs754203 marker probably does not impact the binding of regulatory factors, suggesting that other polymorphic sites underlie the observed associations. Our results provide an important independent replication of previous findings, supporting the existence of CYP46A1 sequence variants that contribute to variability in beta-amyloid metabolism.

A mouse model for α-methylacyl-CoA racemase deficiency: adjustment of bile acid synthesis and intolerance to dietary methyl-branched lipids

alpha-Methylacyl-CoA racemase (Amacr) deficiency in humans leads to sensory motor neuronal and liver abnormalities. The disorder is recessively inherited and caused by mutations in the AMACR gene, which encodes Amacr, an enzyme presumed to be essential for bile acid synthesis and to participate in the degradation of methyl-branched fatty acids. To generate a model to study the pathophysiology in Amacr deficiency we inactivated the mouse Amacr gene. As per human Amacr deficiency, the Amacr(-/-) mice showed accumulation (44-fold) of C27 bile acid precursors and decreased (over 50%) primary (C24) bile acids in bile, serum and liver, however the Amacr(-/-) mice were clinically symptomless. Real-time quantitative PCR analysis showed that, among other responses, the level of mRNA for peroxisomal multifunctional enzyme type 1 (pMFE-1) was increased 3-fold in Amacr(-/-) mice. This enzyme can be placed, together with CYP3A11 and CYP46A1, to make an Amacr-independent pathway for the generation of C24 bile acids. Exposure of Amacr(-/-) mice to a diet supplemented with phytol, a source for branched-chain fatty acids, triggered the development of a disease state with liver manifestations, redefining the physiological significance of Amacr. Amacr is indispensable for the detoxification of dietary methyl-branched lipids and, although it contributes normally to bile acid synthesis from cholesterol, the putative pMFE-1-mediated cholesterol degradation can provide for generation of bile acids, allowing survival without Amacr. Based upon our mouse model, we propose elimination of phytol from the diet of patients suffering from Amacr deficiency.

[Cholesterol and statins in Alzheimer disease]

Two recent observational studies have demonstrated a 60-73% reduction in the prevalence of Alzheimer's disease in patients treated with statins. In two further studies a polymorphism in the CYP46 gene encoding the cholesterol-24 hydroxylase was found to be associated with a significant increase in the risk of late-onset Alzheimer's disease. The question arises whether or not statins may exert a prophylactic effect on the incidence of Alzheimer's disease. Statins pass the blood-brain-barrier to a different degree and may reduce the cerebral cholesterol turnover. Statins may also influence the CSF concentration of tau protein, and, to a minor extent, that of A beta. Further studies are warranted to find out which statins are most suitable for reducing cerebral amyloid metabolism and whether statins may also lower the severity of Alzheimer's disease.