Novel oxysterols observed in tissues and fluids of AY9944-treated rats: a model for Smith-Lemli-Opitz syndrome

The drug release of PLGA-based nanoparticles and their application in treatment of gastrointestinal cancers

The poly (lactic-co-glycolic acid) (PLGA) based nanoparticles have been applied for drug delivery due to their simple preparation, biodegradability, and ideal biocompatibility. In this study, the factors affecting the degradation of PLGA-based nanoparticles are reviewed, encompassing the ratio of PLA to PGA, relative molecular weight, crystallinity, and preparation process of PLGA nanoparticles. The drug release behavior of PLGA-based nanoparticles, such as the degradation environment, encapsulated drug properties of polymers, and drug loading rates, are also discussed. Since gastrointestinal cancer is one of the major global threats to human health, this paper comprehensively summarizes the application of PLGA nanoparticles in gastrointestinal cancers from diagnosis, chemotherapy, radiotherapy, and novel tumor treatment methods (immunotherapy, gene therapy, and photothermal therapy). Finally, the future application of PLGA-based drug delivery systems in treating gastrointestinal cancers is discussed. The bottleneck of application status and the prospect of PLGA-nanoparticles in gastrointestinal tumor application are presented. To truly realize the great and wide application of PLGA-based nanoparticles, collaborative progress in the field of nanomaterials and life sciences is needed.

Enhancing 7-dehydrocholesterol suppresses brain ferroptosis and tissue injury after neonatal hypoxia-ischemia

Neonatal hypoxic-ischemic brain injury (HIBI) results in part from excess reactive oxygen species and iron-dependent lipid peroxidation (i.e. ferroptosis). The vitamin D precursor 7-dehydrocholesterol (7-DHC) may inhibit iron-dependent lipid peroxidation. Primary neurons underwent oxygen and glucose deprivation (OGD) injury and treatment with 7-DHC-elevating medications such as cariprazine (CAR) or vehicle. Postnatal day 9 mice underwent sham surgery or carotid artery ligation and hypoxia and received intraperitoneal CAR. In neurons, CAR administration resulted in significantly increased cell survival compared to vehicle controls, whether administered 48 h prior to or 30 min after OGD, and was associated with increased 7-DHC. In the mouse model, malondialdehyde and infarct area significantly increased after HIBI in the vehicle group, which were attenuated by post-treatment with CAR and were negatively correlated with tissue 7-DHC concentrations. Elevating 7-DHC concentrations with CAR was associated with improved cellular and tissue viability after hypoxic-ischemic injury, suggesting a novel therapeutic avenue.

Chemical Inhibition of Sterol Biosynthesis

Cholesterol is an essential molecule of life, and its synthesis can be inhibited by both genetic and nongenetic mechanisms. Hundreds of chemicals that we are exposed to in our daily lives can alter sterol biosynthesis. These also encompass various classes of FDA-approved medications, including (but not limited to) commonly used antipsychotic, antidepressant, antifungal, and cardiovascular medications. These medications can interfere with various enzymes of the post-lanosterol biosynthetic pathway, giving rise to complex biochemical changes throughout the body. The consequences of these short- and long-term homeostatic disruptions are mostly unknown. We performed a comprehensive review of the literature and built a catalogue of chemical agents capable of inhibiting post-lanosterol biosynthesis. This process identified significant gaps in existing knowledge, which fall into two main areas: mechanisms by which sterol biosynthesis is altered and consequences that arise from the inhibitions of the different steps in the sterol biosynthesis pathway. The outcome of our review also reinforced that sterol inhibition is an often-overlooked mechanism that can result in adverse consequences and that there is a need to develop new safety guidelines for the use of (novel and already approved) medications with sterol biosynthesis inhibiting side effects, especially during pregnancy.

DHCR7 promotes lymph node metastasis in cervical cancer through cholesterol reprogramming-mediated activation of the KANK4/PI3K/AKT axis and VEGF-C secretion

Cervical cancer (CC) patients with lymph node metastasis (LNM) have a poor prognosis. However, the molecular mechanism of LNM in CC is unclear, and there is no effective clinical treatment. Here, we found that 7-dehydrocholesterol reductase (DHCR7), an enzyme that catalyzes the last step of cholesterol synthesis, was upregulated in CC and closely related to LNM. Gain-of-function and loss-of-function experiments proved that DHCR7 promoted the invasion ability of CC cells and lymphangiogenesis in vitro and induced LNM in vivo. The LNM-promoting effect of DHCR7 was partly mediated by upregulating KN motif and ankyrin repeat domains 4 (KANK4) expression and subsequently activating the PI3K/AKT signaling pathway. Alternatively, DHCR7 promoted the secretion of vascular endothelial growth factor-C (VEGF-C), and thereby lymphangiogenesis. Interestingly, cholesterol reprogramming was needed for the DHCR7-mediated promotion of activation of the KANK4/PI3K/AKT axis, VEGF-C secretion, and subsequent LNM. Importantly, treatment with the DHCR7 inhibitors AY9944 and tamoxifen (TAM) significantly inhibited LNM of CC, suggesting the clinical application potential of DHCR7 inhibitors in CC. Collectively, our results uncover a novel molecular mechanism of LNM in CC and identify DHCR7 as a new potential therapeutic target.

Cholic acid increases plasma cholesterol in Smith-Lemli-Opitz syndrome: A pilot study

Background

Smith-Lemli-Opitz syndrome (SLOS) is an inherited disorder of cholesterol biosynthesis associated with congenital malformations, growth delay, intellectual disability and behavior problems. SLOS is caused by bi-allelic mutations in DHCR7, which lead to reduced activity of 7-dehydrocholesterol reductase that catalyzes the last step in cholesterol biosynthesis. Symptoms of SLOS are thought to be due to cholesterol deficiency and accumulation of its precursor 7-dehydrocholesterol (7-DHC) and 8-dehydrocholesterol (8-DHC), and toxic oxysterols. Therapy for SLOS often includes dietary cholesterol supplementation, but lipids are poorly absorbed from the diet, possibly due to impaired bile acid synthesis. We hypothesized that bile acid supplementation with cholic acid would improve dietary cholesterol absorption and raise plasma cholesterol levels.

Methods

Twelve SLOS subjects (10 M, 2F, ages 2-27 years) who had plasma cholesterol ≤125 mg/dL were treated with cholic acid (10 mg/kg/day) divided twice daily for 2 months. Plasma cholesterol, 7-DHC and 8-DHC were measured by GC-MS. Oxysterols were measured by ultra-high-performance LC-MS/MS. Data were analyzed using paired t-tests.

Results

At baseline, plasma cholesterol was 75 ± 24 mg/dL (mean ± SD; range 43-125, n = 12). After 2 months on cholic acid, mean plasma cholesterol increased to 97 ± 29 mg/dL (p = 0.011). Eleven of 12 subjects showed an increase in plasma cholesterol that varied from 3.8% to 85.7% (mean 38.7 ± 23.3%). 7-Hydroxycholesterol decreased by 20.6% on average (p = 0.013) but no significant changes were seen in 7-DHC or 8-DHC. Mean body weight tended to increase (3.6% p = 0.069). Subjects tolerated cholic acid well and experienced no drug-related adverse events.

Conclusions

In this pilot study, cholic acid supplementation was well tolerated and safe and resulted in an increase in plasma cholesterol in most SLOS subjects. Further controlled longitudinal studies are needed to look for the sustainability of the biochemical effect and possible clinical benefits.

Cholesterol regulates insulin-induced mTORC1 signaling

The rapid activation of the crucial kinase mechanistic target of rapamycin complex-1 (mTORC1) by insulin is key to cell growth in mammals, but the regulatory factors remain unclear. Here, we demonstrate that cholesterol plays a crucial role in the regulation of insulin-stimulated mTORC1 signaling. The rapid progression of insulin-induced mTORC1 signaling declines in sterol-depleted cells and restores in cholesterol-repleted cells. In insulin-stimulated cells, cholesterol promotes recruitment of mTORC1 onto lysosomes without affecting insulin-induced dissociation of the TSC complex from lysosomes, thereby enabling complete activation of mTORC1. We also show that under prolonged starvation conditions, cholesterol coordinates with autophagy to support mTORC1 reactivation on lysosomes thereby restoring insulin-responsive mTORC1 signaling. Furthermore, we identify that fibroblasts from individuals with Smith-Lemli-Opitz Syndrome (SLOS) and model HeLa-SLOS cells, which are deficient in cholesterol biosynthesis, exhibit defects in the insulin-mTORC1 growth axis. These defects are rescued by supplementation of exogenous cholesterol or by expression of constitutively active Rag GTPase, a downstream activator of mTORC1. Overall, our findings propose novel signal integration mechanisms to achieve spatial and temporal control of mTORC1-dependent growth signaling and their aberrations in disease.

MALDI-IM-MS Imaging of Brain Sterols and Lipids in a Mouse Model of Smith-Lemli-Opitz Syndrome

Smith-Lemli-Opitz syndrome (SLOS) is a neurodevelopmental disorder caused by genetic mutations in the DHCR7 gene, encoding the enzyme 3β-hydroxysterol-Δ7-reductase (DHCR7) that catalyzes the last step of cholesterol synthesis. The resulting deficiency in cholesterol and accumulation of its precursor, 7-dehydrocholesterol (7-DHC), have a profound impact on brain development, which manifests as developmental delay, cognitive impairment, and behavioral deficits. To understand how the brain regions are differentially affected by the defective Dhcr7, we aim to map the regional distribution of sterols and other lipids in neonatal brains from a Dhcr7-KO mouse model of SLOS, using mass spectrometry imaging (MSI). MSI enables spatial localization of biomolecules in situ on the surface of a tissue section, which is particularly useful for mapping the changes that occur within a metabolic disorder such as SLOS, and in an anatomically complex organ such as the brain. In this work, using MALDI-ion mobility (IM)-MSI, we successfully determined the regional distribution of features that correspond to cholesterol, 7-DHC/desmosterol, and the precursor of desmosterol, 7-dehydrodesmosterol, in WT and Dhcr7-KO mice. Interestingly, we also observed m/z values that match the major oxysterol metabolites of 7-DHC (DHCEO and hydroxy-7-DHC), which displayed similar patterns as 7-DHC. We then identified brain lipids using m/z and CCS at the Lipid Species-level and curated a database of MALDIIM-MS-derived lipid CCS values. Subsequent statistical analysis of regions-of-interest allowed us to identify differentially expressed lipids between Dhcr7-KO and WT brains, which could contribute to defects in myelination, neurogenesis, neuroinflammation, and learning and memory in SLOS.

Chronic Aripiprazole and Trazodone Polypharmacy Effects on Systemic and Brain Cholesterol Biosynthesis

The concurrent use of several medications is a common practice in the treatment of complex psychiatric conditions. One such commonly used combination is aripiprazole (ARI), an antipsychotic, and trazodone (TRZ), an antidepressant. In addition to their effects on dopamine and serotonin systems, both of these compounds are inhibitors of the 7-dehydrocholesterol reductase (DHCR7) enzyme. To evaluate the systemic and nervous system distribution of ARI and TRZ and their effects on cholesterol biosynthesis, adult mice were treated with both ARI and TRZ for 21 days. The parent drugs, their metabolites, and sterols were analyzed in the brain and various organs of mice using LC-MS/MS. The analyses revealed that ARI, TRZ, and their metabolites were readily detectable in the brain and organs, leading to changes in the sterol profile. The levels of medications, their metabolites, and sterols differed across tissues with notable sex differences. Female mice showed higher turnover of ARI and more cholesterol clearance in the brain, with several post-lanosterol intermediates significantly altered. In addition to interfering with sterol biosynthesis, ARI and TRZ exposure led to decreased ionized calcium-binding adaptor molecule 1 (IBA1) and increased DHCR7 protein expression in the cortex. Changes in sterol profile have been also identified in the spleen, liver, and serum, underscoring the systemic effect of ARI and TRZ on sterol biosynthesis. Long-term use of concurrent ARI and TRZ warrants further studies to fully evaluate the lasting consequences of altered sterol biosynthesis on the whole body.

Zika virus non-structural protein 4B interacts with DHCR7 to facilitate viral infection

Zika virus (ZIKV) evolves non-structural proteins to evade immune response and ensure efficient replication in the host cells. Cholesterol metabolic enzyme 7-dehydrocholesterol reductase (DHCR7) was recently reported to impact innate immune responses in ZIKV infection. However, the vital non-structural protein and mechanisms involved in DHCR7-mediated viral evasion are not well elucidated. In this study, we demonstrated that ZIKV infection facilitated DHCR7 expression. Notably, the upregulated DHCR7 in turn facilitated ZIKV infection and blocking DHCR7 suppressed ZIKV infection. Mechanically, ZIKV non-structural protein 4B (NS4B) interacted with DHCR7 to induce DHCR7 expression. Moreover, DHCR7 inhibited TANK-binding kinase 1 (TBK1) and interferon regulatory factor 3 (IRF3) phosphorylation, which resulted in the reduction of interferon-beta (IFN-β) and interferon-stimulated genes (ISGs) productions. Therefore, we propose that ZIKV NS4B binds to DHCR7 to repress TBK1 and IRF3 activation, which in turn inhibits IFN-β and ISGs, and thereby facilitating ZIKV evasion. This study broadens the insights on how viral non-structural proteins antagonize innate immunity to facilitate viral infection via cholesterol metabolic enzymes and intermediates.

Dose-Response Effects of 7-Dehydrocholesterol Reductase Inhibitors on Sterol Profiles and Vesicular Stomatitis Virus Replication

Cholesterol is ubiquitous in cells; it plays a critical role in membrane structure and transport as well as in intracellular trafficking processes. There are suggestions that cholesterol metabolism is linked to innate immunity with inhibitors of DHCR7, the last enzyme in the cholesterol pathway, suggested to have potential as viral therapeutics nearly a decade ago. In fact, there are a number of highly prescribed pharmaceuticals that are off-target inhibitors of DHCR7, causing increased cellular levels of 7-dehydrodesmosterol (7-DHD) and 7-dehydrocholesterol (7-DHC). We report here dose-response studies of six such inhibitors on late-stage cholesterol biosynthesis in Neuro2a cells as well as their effect on infection of vesicular stomatitis virus (VSV). Four of the test compounds are FDA-approved drugs (cariprazine, trazodone, metoprolol, and tamoxifen), one (ifenprodil) has been the object of a recent Phase 2b COVID trial, and one (AY9944) is an experimental compound that has seen extensive use as a DHCR7 inhibitor. The three FDA-approved drugs inhibit replication of a GFP-tagged VSV with efficacies that mirror their effect on DHCR7. Ifenprodil and AY9944 have complex inhibitory profiles, acting on both DHCR7 and DHCR14, while tamoxifen does not inhibit DHCR7 and is toxic to Neuro2a at concentrations where it inhibits the Δ7-Δ8 isomerase of the cholesterol pathway. VSV itself affects the sterol profile in Neuro2a cells, showing a dose-response increase of dehydrolathosterol and lathosterol, the substrates for DHCR7, with a corresponding decrease in desmosterol and cholesterol. 7-DHD and 7-DHC are orders of magnitude more vulnerable to free radical chain oxidation than other sterols as well as polyunsaturated fatty esters, and the effect of these sterols on viral infection is likely a reflection of this fact of Nature.

7-Dehydrocholesterol Encapsulated Polymeric Nanoparticles As a Radiation-Responsive Sensitizer for Enhancing Radiation Therapy

Therapeutics that can be activated by radiation in situ to enhance the efficacy of radiotherapy are highly desirable. Herein, 7-Dehydrocholesterol (7-DHC), a biosynthetic precursor of cholesterol, as a radiosensitizer, exploiting its ability to propagate the free radical chain reaction is explored. The studies show that 7-DHC can react with radiation-induced reactive oxygen species and in turn promote lipid peroxidation, double-strand breaks, and mitochondrial damage in cancer cells. For efficient delivery, 7-DHC is encapsulated into poly(lactic-co-glycolic acid) nanoparticles, forming 7-DHC@PLGA NPs. When tested in CT26 tumor bearing mice, 7-DHC@PLGA NPs significantly enhanced the efficacy of radiotherapy, causing complete tumor eradication in 30% of the treated animals. After treatment, 7-DHC is converted to cholesterol, causing no detectable side effects or hypercalcemia. 7-DHC@PLGA NPs represent a radiation-responsive sensitizer with great potential in clinical translation.

Biochemical and Clinical Effects of Vitamin E Supplementation in Hungarian Smith-Lemli-Opitz Syndrome Patients

Smith-Lemli-Opitz syndrome (SLOS) is a severe monogenic disorder resulting in low cholesterol and high 7-dehydrocholesterol (7-DHC) levels. 7-DHC-derived oxysterols likely contribute to disease pathophysiology, and thus antioxidant treatment might be beneficial because of high oxidative stress. In a three-year prospective study, we investigated the effects of vitamin E supplementation in six SLOS patients already receiving dietary cholesterol treatment. Plasma vitamin A and E concentrations were determined by the high-performance liquid chromatography (HPLC) method. At baseline, plasma 7-DHC, 8-dehydrocholesterol (8-DHC) and cholesterol levels were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. The clinical effect of the supplementation was assessed by performing structured parental interviews. At baseline, patients were characterized by low or low-normal plasma vitamin E concentrations (7.19-15.68 μmol/L), while vitamin A concentrations were found to be normal or high (1.26-2.68 μmol/L). Vitamin E supplementation resulted in correction or significant elevation of plasma vitamin E concentration in all patients. We observed reduced aggression, self-injury, irritability, hyperactivity, attention deficit, repetitive behavior, sleep disturbance, skin photosensitivity and/or eczema in 3/6 patients, with notable individual variability. Clinical response to therapy was associated with a low baseline 7-DHC + 8-DHC/cholesterol ratio (0.2-0.4). We suggest that determination of vitamin E status is important in SLOS patients. Supplementation of vitamin E should be considered and might be beneficial.

Sterol and oxysterol synthases near the ciliary base activate the Hedgehog pathway

Vertebrate Hedgehog signals are transduced through the primary cilium, a specialized lipid microdomain that is required for Smoothened activation. Cilia-associated sterol and oxysterol lipids bind to Smoothened to activate the Hedgehog pathway, but how ciliary lipids are regulated is incompletely understood. Here we identified DHCR7, an enzyme that produces cholesterol, activates the Hedgehog pathway, and localizes near the ciliary base. We found that Hedgehog stimulation negatively regulates DHCR7 activity and removes DHCR7 from the ciliary microenvironment, suggesting that DHCR7 primes cilia for Hedgehog pathway activation. In contrast, we found that Hedgehog stimulation positively regulates the oxysterol synthase CYP7A1, which accumulates near the ciliary base and produces oxysterols that promote Hedgehog signaling in response to pathway activation. Our results reveal that enzymes involved in lipid biosynthesis in the ciliary microenvironment promote Hedgehog signaling, shedding light on how ciliary lipids are established and regulated to transduce Hedgehog signals.

Sterol Biosynthesis Inhibition in Pregnant Women Taking Prescription Medications

Sterol biosynthesis is a critical homeostatic mechanism of the body. Sterol biosynthesis begins during early embryonic life and continues throughout life. Many commonly used medications, prescribed >200 million times in the United States annually, have a sterol biosynthesis inhibition side effect. Using our high-throughput LC-MS/MS method, we assessed the levels of post-lanosterol sterol intermediates (lanosterol, desmosterol, and 7-dehydrocholesterol (7-DHC)) and cholesterol in 1312 deidentified serum samples from pregnant women. 302 samples showing elevated 7-DHC were analyzed for the presence of 14 medications known to inhibit the 7-dehydrocholesterol reductase enzyme (DHCR7) and increase 7-DHC. Of the 302 samples showing 7-DHC elevation, 43 had detectable levels of prescription medications with a DHCR7-inhibiting side effect. Taking more than one 7-DHC-elevating medication in specific combinations (polypharmacy) might exacerbate the effect on 7-DHC levels in pregnant women, suggesting a potentially additive or synergistic effect. As 7-DHC and 7-DHC-derived oxysterols are toxic, and as DHCR7-inhibiting medications are considered teratogens, our findings raise potential concerns regarding the use of prescription medication with a DHCR7-inhibiting side effect during pregnancy. The use of prescription medications during pregnancy is sometimes unavoidable, but choosing a medication without a DHCR7-inhibiting side effect might lead to a heathier pregnancy and prevent putatively adverse outcomes for the developing offspring.

Cholesterol homeostasis in the vertebrate retina: biology and pathobiology

Cholesterol is a quantitatively and biologically significant constituent of all mammalian cell membrane, including those that comprise the retina. Retinal cholesterol homeostasis entails the interplay between de novo synthesis, uptake, intraretinal sterol transport, metabolism, and efflux. Defects in these complex processes are associated with several congenital and age-related disorders of the visual system. Herein, we provide an overview of the following topics: (a) cholesterol synthesis in the neural retina; (b) lipoprotein uptake and intraretinal sterol transport in the neural retina and the retinal pigment epithelium (RPE); (c) cholesterol efflux from the neural retina and the RPE; and (d) biology and pathobiology of defects in sterol synthesis and sterol oxidation in the neural retina and the RPE. We focus, in particular, on studies involving animal models of monogenic disorders pertinent to the above topics, as well as in vitro models using biochemical, metabolic, and omic approaches. We also identify current knowledge gaps and opportunities in the field that beg further research in this topic area.

Oxysterols and retinal degeneration

Retinal degeneration, characterised by the progressive death of retinal neurons, is the most common cause of visual impairment. Oxysterols are the cholesterol derivatives produced via enzymatic and/or free radical oxidation that regulate cholesterol homeostasis in the retina. Preclinical and clinical studies have suggested a connection between oxysterols and retinal degeneration. Here, we summarise early and recent work related to retina oxysterol-producing enzymes and the distribution of oxysterols in the retina. We examine the impact of loss of oxysterol-producing enzymes on retinal pathology and explore the molecular mechanisms associated with the toxic or protective roles of individual oxysterols in different types of retinal degeneration. We conclude that increased efforts to better understand the oxysterol-associated pathophysiology will help in the development of effective retinal degeneration therapies. LINKED ARTICLES: This article is part of a themed issue on Oxysterols, Lifelong Health and Therapeutics. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.16/issuetoc.

Transcriptomic Changes Associated with Loss of Cell Viability Induced by Oxysterol Treatment of a Retinal Photoreceptor-Derived Cell Line: An In Vitro Model of Smith-Lemli-Opitz Syndrome

Smith–Lemli–Opitz Syndrome (SLOS) results from mutations in the gene encoding the enzyme DHCR7, which catalyzes conversion of 7-dehydrocholesterol (7DHC) to cholesterol (CHOL). Rats treated with a DHCR7 inhibitor serve as a SLOS animal model, and exhibit progressive photoreceptor-specific cell death, with accumulation of 7DHC and oxidized sterols. To understand the basis of this cell type specificity, we performed transcriptomic analyses on a photoreceptor-derived cell line (661W), treating cells with two 7DHC-derived oxysterols, which accumulate in tissues and bodily fluids of SLOS patients and in the rat SLOS model, as well as with CHOL (negative control), and evaluated differentially expressed genes (DEGs) for each treatment. Gene enrichment analysis and compilation of DEG sets indicated that endoplasmic reticulum stress, oxidative stress, DNA damage and repair, and autophagy were all highly up-regulated pathways in oxysterol-treated cells. Detailed analysis indicated that the two oxysterols exert their effects via different molecular mechanisms. Changes in expression of key genes in highlighted pathways (Hmox1, Ddit3, Trib3, and Herpud1) were validated by immunofluorescence confocal microscopy. The results extend our understanding of the pathobiology of retinal degeneration and SLOS, identifying potential new druggable targets for therapeutic intervention into these and other related orphan diseases.

Prescription Medications Alter Neuronal and Glial Cholesterol Synthesis

Mouse brain contains over 100 million neuronal, glial, and other support cells. Developing neurons and astrocytes synthesize their own cholesterol, and disruption of this process can occur by both genetic and chemical mechanisms. In this study we have exposed cultured murine neurons and astrocytes to six different prescription medications that cross the placenta and blood-brain barriers and analyzed the effects of these drugs on cholesterol biosynthesis by an LC-MS/MS protocol that assays 14 sterols and 7 oxysterols in a single run. Three antipsychotics (haloperidol, cariprazine, aripiprazole), two antidepressants (trazodone and sertraline), and an antiarhythmic (amiodarone) inhibited one or more sterol synthesis enzymes. The result of the exposures was a dose-dependent increase in levels of various sterol intermediates and a decreased level of cholesterol in the cultured cells. Four prescription medications (haloperidol, aripiprazole, cariprazine, and trazodone) acted primarily on the DHCR7 enzyme. The result of this exposure was an increase in 7-dehydrocholesterol in neurons and astrocytes to levels that were comparable to those found in cultured neurons and astrocytes from transgenic mice that carried a Dhcr7 pathogenic mutation modeling the neurodevelopmental disorder Smith-Lemli-Opitz syndrome.

Visualisation of cholesterol and ganglioside GM1 in zebrafish models of Niemann-Pick type C disease and Smith-Lemli-Opitz syndrome using light sheet microscopy

Lysosomal storage diseases are the most common cause of neurodegeneration in children. They are characterised at the cellular level by the accumulation of storage material within lysosomes. There are very limited therapeutic options, and the search for novel therapies has been hampered as few good small animal models are available. Here, we describe the use of light sheet microscopy to assess lipid storage in drug and morpholino induced zebrafish models of two diseases of cholesterol homeostasis with lysosomal dysfunction: First, Niemann–Pick type C disease (NPC), caused by mutations in the lysosomal transmembrane protein NPC1, characterised by intralysosomal accumulation of cholesterol and several other lipids. Second, Smith–Lemli–Opitz syndrome (SLOS), caused by mutations in 7-dehydrocholesterol reductase, which catalyses the last step of cholesterol biosynthesis and is characterised by intralysosomal accumulation of dietary cholesterol. This is the first description of a zebrafish SLOS model. We find that zebrafish accurately model lysosomal storage and disease-specific phenotypes in both diseases. Increased cholesterol and ganglioside GM1 were observed in sections taken from NPC model fish, and decreased cholesterol in SLOS model fish, but these are of limited value as resolution is poor, and accurate anatomical comparisons difficult. Using light sheet microscopy, we were able to observe lipid changes in much greater detail and identified an unexpected accumulation of ganglioside GM1 in SLOS model fish. Our data demonstrate, for the first time in zebrafish, the immense potential that light sheet microscopy has in aiding the resolution of studies involving lysosomal and lipid disorders.

Drug-induced lenticular opacity and accumulation of cholesterol-related substances in the lens cortex of dogs

TP0446131, developed as an antidepressant agent, was found to cause lenticular opacity in a 13-week repeated-dose study in dogs. Histopathologically, the lenticular opacity was observed as a degeneration of the lens fibers, characterized by irregularity in the ordered arrangement of the fibers which is necessary to maintain the transparency of the lens, and was considered to manifest clinically as cataract. To evaluate the development mechanism of the lenticular opacity, the chemical constituents of the lens, which is known to be associated with the development of cataract, were examined. The results of liquid chromatography-tandem mass spectrometry analysis revealed an increase in the amplitudes of 3 unknown peaks in a dose- and time-dependent manner in the lens, with no remarkable changes in the other chemical components tested. In addition, the content of cholesterol, alterations of which have been reported to be associated with cataract, remained unchanged. The mass spectral data and chromatographic behavior of the 3 peaks indicated that these peaks corresponded to sterol-related substances, and that one of them was 7-dehydrocholesterol, a precursor of cholesterol biosynthesis. This finding suggested that TP0446131 exerts some effects on the cholesterol biosynthesis pathway, which could be involved in the development of the cataracts. Furthermore, increases in the levels of these sterol-related substances were also detected in the serum, and were, in fact, noted prior to the onset of the cataract, suggesting the possibility that these substances in the serum could be used as potential safety biomarkers for predicting the onset of cataract induced by TP0446131.

Reactive Sterol Electrophiles: Mechanisms of Formation and Reactions with Proteins and Amino Acid Nucleophiles

Radical-mediated lipid oxidation and the formation of lipid hydroperoxides has been a focal point in the investigation of a number of human pathologies. Lipid peroxidation has long been linked to the inflammatory response and more recently, has been identified as the central tenet of the oxidative cell death mechanism known as ferroptosis. The formation of lipid electrophile-protein adducts has been associated with many of the disorders that involve perturbations of the cellular redox status, but the identities of adducted proteins and the effects of adduction on protein function are mostly unknown. Both cholesterol and 7-dehydrocholesterol (7-DHC), which is the immediate biosynthetic precursor to cholesterol, are oxidizable by species such as ozone and oxygen-centered free radicals. Product mixtures from radical chain processes are particularly complex, with recent studies having expanded the sets of electrophilic compounds formed. Here, we describe recent developments related to the formation of sterol-derived electrophiles and the adduction of these electrophiles to proteins. A framework for understanding sterol peroxidation mechanisms, which has significantly advanced in recent years, as well as the methods for the study of sterol electrophile-protein adduction, are presented in this review.

Maternal cariprazine exposure inhibits embryonic and postnatal brain cholesterol biosynthesis

Cariprazine (CAR) is a strong inhibitor of the Dhcr7 enzyme, the last enzyme in the cholesterol biosynthesis pathway. We assessed the effects of CAR on maternally exposed Dhcr7^+/- and wild-type mouse offspring, and tested the biochemical effects of CAR in human serum samples. Dhcr7^+/- and wild-type time-pregnant mice were exposed to vehicle or 0.2 mg/kg CAR from E12 to E19. Levels of CAR, CAR metabolites, sterols, and oxysterols were measured in the brain of maternally exposed offspring at various time points using LC-MS/MS. Embryonic exposure to CAR significantly increased levels of 7-DHC in all organs of exposed embryos, with a particularly strong effect in the brain. Detectable levels of CAR and elevated 7-DHC were observed in the brain of newborn pups 14 days after drug exposure. In addition, CAR altered sterol metabolism in all animals analyzed, with the strongest effect on the brain of Dhcr7^+/- pups born to Dhcr7^+/- dams. Furthermore, CAR elevated toxic oxysterols in the brain of maternally exposed Dhcr7^+/- offspring to levels approaching those seen in a mouse model of Smith-Lemli-Opitz syndrome. Finally, we observed that patients taking CAR have elevated 7-DHC in their serum. In summary, maternal DHCR7 heterozygosity, combined with offspring DHCR7 heterozygosity might represent a vulnerability factor to medications that interfere with sterol biosynthesis. Due to the conserved sterol biosynthesis between mice and humans, we suggest that the 1-3% of patient population with single-allele DHCR7 mutations might not be ideal candidates for CAR use, especially if they are nursing, pregnant or plan to become pregnant.

Targeting 7-Dehydrocholesterol Reductase Integrates Cholesterol Metabolism and IRF3 Activation to Eliminate Infection

Recent work suggests that cholesterol metabolism impacts innate immune responses against infection. However, the key enzymes or the natural products and mechanisms involved are not well elucidated. Here, we have shown that upon DNA and RNA viral infection, macrophages reduced 7-dehydrocholesterol reductase (DHCR7) expression. DHCR7 deficiency or treatment with the natural product 7-dehydrocholesterol (7-DHC) could specifically promote phosphorylation of IRF3 (not TBK1) and enhance type I interferon (IFN-I) production in macrophages. We further elucidated that viral infection or 7-DHC treatment enhanced AKT3 expression and activation. AKT3 directly bound and phosphorylated IRF3 at Ser385, together with TBK1-induced phosphorylation of IRF3 Ser386, to achieve IRF3 dimerization. Deletion of DHCR7 and the DHCR7 inhibitors including AY9944 and the chemotherapy drug tamoxifen promoted clearance of Zika virus and multiple viruses in vitro or in vivo. Taken together, we propose that the DHCR7 inhibitors and 7-DHC are potential therapeutics against emerging or highly pathogenic viruses.

Omics analysis of oxysterols to better understand their pathophysiological role

High amounts of cholesterol have been definitely associated with the pathogenesis of several diseases, including metabolic and neurodegenerative disorders, cardiovascular diseases, and cancer. In all these pathologies the exacerbation of pro-oxidant and inflammatory responses is a consistent feature. In this scenario, species derived from enzymatic and non-enzymatic cholesterol oxidation, namely oxysterols, are strongly suspected to play a primary role. The consideration of these bioactive lipids is therefore helpful in investigating pathological mechanisms and may also acquire clinical value for the diagnosis and treatment of diseases. For this purpose and considering that a great number of oxysterols may be present together in the body, the employment of lipidomics technology certainly represents a powerful strategy for the simultaneous detection and characterization of these compounds in biological specimens. In this review, we will discuss the applicability of the lipidomics approach in the study of the association between oxysterols and diseases.

Multi-omics investigation reveals benzalkonium chloride disinfectants alter sterol and lipid homeostasis in the mouse neonatal brain

Lipids are critical for neurodevelopment; therefore, disruption of lipid homeostasis by environmental chemicals is expected to have detrimental effects on this process. Previously, we demonstrated that the benzalkonium chlorides (BACs), a class of commonly used disinfectants, alter cholesterol biosynthesis and lipid homeostasis in neuronal cell cultures in a manner dependent on their alkyl chain length. However, the ability of BACs to reach the neonatal brain and alter sterol and lipid homeostasis during neurodevelopment in vivo has not been characterized. Therefore, the goal of this study was to use targeted and untargeted mass spectrometry and transcriptomics to investigate the effect of BACs on sterol and lipid homeostasis, and to predict the mechanism of toxicity of BACs on neurodevelopmental processes. After maternal dietary exposure to 120 mg BAC/kg body weight/day, we quantified BAC levels in the mouse neonatal brain, demonstrating for the first time that BACs can cross the blood-placental barrier and enter the developing brain. Transcriptomic analysis of neonatal brains using RNA sequencing revealed alterations in canonical pathways related to cholesterol biosynthesis, liver X receptor-retinoid X receptor (LXR/RXR) signaling, and glutamate receptor signaling. Mass spectrometry analysis revealed decreases in total sterol levels and downregulation of triglycerides and diglycerides, which were consistent with the upregulation of genes involved in sterol biosynthesis and uptake as well as inhibition of LXR signaling. In conclusion, these findings demonstrate that BACs target sterol and lipid homeostasis and provide new insights for the possible mechanisms of action of BACs as developmental neurotoxicants.

Oxysterols as a biomarker in diseases

Cholesterol is one of the most important chemical substances as a structural element in human cells, and it is very susceptible to oxidation reactions that form oxysterol. Oxysterols exhibit almost the exact structure as cholesterol and a cholesterol precursor (7-dehydrocholesterol) with an additional hydroxyl, epoxy or ketone moiety. The oxidation reaction is performed via an enzymatic or non-enzymatic mechanism. The wide array of enzymatic oxysterols encountered in the human body varies in origin and function. Oxysterols establish a concentration equilibrium in human body fluids. Disease may alter the equilibrium, and oxysterols may be used as a diagnostic tool. The current review presents the possibility of using non-enzymatic oxysterols and disturbances in enzymatic oxysterol equilibrium in the human body as a potential biomarker for diagnosing and/or monitoring of the progression of various diseases.

Liver Transplant and Improvements in Cholesterol Biosynthesis Defects: A Case Report of Smith-Lemli-Opitz Syndrome

Smith-Lemli-Opitz syndrome is an autosomal recessive metabolic disease characterized by mental retardation and multiple congenital anomalies. The main pathology is the lack of the enzyme 3β-hydroxysterol Δ7-reductase, which is the last enzymatic step in cholesterol synthesis, ending with a low cholesterol level. Cholesterol is vitally important in cell membranes and myelination of the nervous system. The cholesterol level affects many systems of the body, especially the nervous system. The cause of liver involvement in Smith-Lemli-Opitz syndrome is unclear, and many hypotheses have been suggested. Here, we present the early results of a patient with Smith-Lemli-Opitz syndrome who underwent living-donor liver transplant due to cirrhosis. As a result of liver transplant, normal cholesterol levels were shown, as well as improvements in the patient's neurodevelopment and behavior. Early liver transplant may be considered for patients with a defect of cholesterol biosynthesis, even in the absence of cirrhosis, and may be a future treatment option to prevent risks of neurologic deterioration.

Human kidney on a chip assessment of polymyxin antibiotic nephrotoxicity

Drug-induced kidney injury, largely caused by proximal tubular intoxicants, limits development and clinical use of new and approved drugs. Assessing preclinical nephrotoxicity relies on animal models that are frequently insensitive; thus, potentially novel techniques - including human microphysiological systems, or "organs on chips" - are proposed to accelerate drug development and predict safety. Polymyxins are potent antibiotics against multidrug-resistant microorganisms; however, clinical use remains restricted because of high risk of nephrotoxicity and limited understanding of toxicological mechanisms. To mitigate risks, structural analogs of polymyxins (NAB739 and NAB741) are currently in clinical development. Using a microphysiological system to model human kidney proximal tubule, we exposed cells to polymyxin B (PMB) and observed significant increases of injury signals, including kidney injury molecule-1 KIM-1and a panel of injury-associated miRNAs (each P < 0.001). Surprisingly, transcriptional profiling identified cholesterol biosynthesis as the primary cellular pathway induced by PMB (P = 1.22 ×10-16), and effluent cholesterol concentrations were significantly increased after exposure (P < 0.01). Additionally, we observed no upregulation of the nuclear factor (erythroid derived-2)-like 2 pathway, despite this being a common pathway upregulated in response to proximal tubule toxicants. In contrast with PMB exposure, minimal changes in gene expression, injury biomarkers, and cholesterol concentrations were observed in response to NAB739 and NAB741. Our findings demonstrate the preclinical safety of NAB739 and NAB741 and reveal cholesterol biosynthesis as a potentially novel pathway for PMB-induced injury. To our knowledge, this is the first demonstration of a human-on-chip platform used for simultaneous safety testing of new chemical entities and defining unique toxicological pathway responses of an FDA-approved molecule.

Oxysterols and Retinal Degeneration in a Rat Model of Smith-Lemli-Opitz Syndrome: Implications for an Improved Therapeutic Intervention

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive human disease caused by mutations in the gene encoding 7-dehydrocholesterol (7DHC) reductase (DHCR7), resulting in abnormal accumulation of 7DHC and reduced levels of cholesterol in bodily tissues and fluids. A rat model of the disease has been created by treating normal rats with the DHCR7 inhibitor, AY9944, which causes progressive, irreversible retinal degeneration. Herein, we review the features of this disease model and the evidence linking 7DHC-derived oxysterols to the pathobiology of the disease, with particular emphasis on the associated retinal degeneration. A recent study has shown that treating the rat model with cholesterol plus suitable antioxidants completely prevents the retinal degeneration. These findings are discussed with regard to their translational implications for developing an improved therapeutic intervention for SLOS over the current standard of care.

Identification and characterization of prescription drugs that change levels of 7-dehydrocholesterol and desmosterol

Regulating blood cholesterol (Chol) levels by pharmacotherapy has successfully improved cardiovascular health. There is growing interest in the role of Chol precursors in the treatment of diseases. One sterol precursor, desmosterol (Des), is a potential pharmacological target for inflammatory and neurodegenerative disorders. However, elevating levels of the precursor 7-dehydrocholesterol (7-DHC) by inhibiting the enzyme 7-dehydrocholesterol reductase is linked to teratogenic outcomes. Thus, altering the sterol profile may either increase risk toward an adverse outcome or confer therapeutic benefit depending on the metabolite affected by the pharmacophore. In order to characterize any unknown activity of drugs on Chol biosynthesis, a chemical library of Food and Drug Administration-approved drugs was screened for the potential to modulate 7-DHC or Des levels in a neural cell line. Over 20% of the collection was shown to impact Chol biosynthesis, including 75 compounds that alter 7-DHC levels and 49 that modulate Des levels. Evidence is provided that three tyrosine kinase inhibitors, imatinib, ponatinib, and masitinib, elevate Des levels as well as other substrates of 24-dehydrocholesterol reductase, the enzyme responsible for converting Des to Chol. Additionally, the mechanism of action for ponatinib and masitinib was explored, demonstrating that protein levels are decreased as a result of treatment with these drugs.

Lipid-derived and other oxidative modifications of retinal proteins in a rat model of Smith-Lemli-Opitz syndrome

Oxidative modification of proteins can perturb their structure and function, often compromising cellular viability. Such modifications include lipid-derived adducts (e.g., 4-hydroxynonenal (HNE) and carboxyethylpyrrole (CEP)) as well as nitrotyrosine (NTyr). We compared the retinal proteome and levels of such modifications in the AY9944-treated rat model of Smith-Lemli-Opitz syndrome (SLOS), in comparison to age-matched controls. Retinas harvested at 3 months of age were either subjected to proteomic analysis or to immuno-slot blot analysis, the latter probing blots with antibodies raised against HNE, CEP, and NTyr, followed by quantitative densitometry. HNE modification of retinal proteins was markedly (>9-fold) higher in AY9944-treated rats compared to controls, whereas CEP modification was only modestly (≤2-fold) greater, and NTyr modification was minimal and exhibited no difference as a function of AY9944 treatment. Anti-HNE immunoreactivity was greatest in the plexiform and ganglion cell layers, but also present in the RPE, choroid, and photoreceptor outer segment layer in AY9944-treated rats; control retinas showed minimal HNE labeling. 1D-PAGE/Western blot analysis of rod outer segment (ROS) membranes revealed HNE modification of both opsin and β-transducin. Proteomic analysis revealed the differential expression of several retinal proteins as a consequence of AY9944 treatment. Upregulated proteins included those involved in chaperone/protein folding, oxidative and cellular stress responses, transcriptional regulation, and energy production. βA3/A1 Crystallin, which has a role in regulation of lysosomal acidification, was down-regulated. Hence, oxidative modification of retinal proteins occurs in the SLOS rat model, in addition to the previously described oxidation of lipids. The results are discussed in the context of the histological and physiological changes that occur in the retina in the SLOS rat model.

Compromised phagosome maturation underlies RPE pathology in cell culture and whole animal models of Smith-Lemli-Opitz Syndrome

Treatment of rats with the cholesterol pathway inhibitor AY9944 produces an animal model of Smith-Lemli-Opitz syndrome (SLOS), an autosomal recessive disease caused by defective cholesterol synthesis. This SLOS rat model undergoes progressive and irreversible degeneration of the neural retina, with associated pathological features of the retinal pigmented epithelium (RPE). Here, we provide further insights into the mechanism involved in the RPE pathology. In the SLOS rat model, markedly increased RPE apical autofluorescence is observed, compared to untreated animals, which correlates with increased levels of A2E and other bisretinoids. Utilizing cultured human induced pluripotent stem cell (iPSC)- derived SLOS RPE cells, we found significantly elevated steady-state levels of 7-dehydrocholesterol (7DHC) and decreased cholesterol levels (key biochemical hallmarks of SLOS). Western blot analysis revealed altered levels of the macroautophagy/autophagy markers MAP1LC3B-II and SQSTM1/p62, and build-up of ubiquitinated proteins. Accumulation of immature autophagosomes was accompanied by inefficient degradation of phagocytized, exogenously supplied retinal rod outer segments (as evidenced by persistence of the C-terminal 1D4 epitope of RHO [rhodopsin]) in SLOS RPE compared to iPSC-derived normal human control. SLOS RPE cells exhibited lysosomal pH levels and CTSD activity within normal physiological limits, thus discounting the involvement of perturbed lysosomal function. Furthermore, 1D4-positive phagosomes that accumulated in the RPE in both pharmacological and genetic rodent models of SLOS failed to fuse with lysosomes. Taken together, these observations suggest that defective phagosome maturation underlies the observed RPE pathology. The potential relevance of these findings to SLOS and the requirement of cholesterol for phagosome maturation are discussed.

Dichlorophenyl piperazines, including a recently-approved atypical antipsychotic, are potent inhibitors of DHCR7, the last enzyme in cholesterol biosynthesis

While antipsychotic medications provide important relief from debilitating psychotic symptoms, they also have significant adverse side effects, which might have relevant impact on human health. Several research studies, including ours, have shown that commonly used antipsychotics such as haloperidol and aripiprazole affect cholesterol biosynthesis at the conversion of 7-dehydrocholesterol (7-DHC) to cholesterol. This transformation is promoted by the enzyme DHCR7 and its inhibition causes increases in plasma and tissue levels of 7-DHC. The inhibition of this enzymatic step by mutations in the Dhcr7 gene leads to Smith-Lemli-Opitz syndrome, a devastating human condition that can be replicated in rats by small molecule inhibitors of DHCR7. The fact that two compounds, brexpiprazole and cariprazine, that were recently approved by the FDA have substructural elements in common with the DHCR7 inhibitor aripiprazole, prompted us to evaluate the effect of brexpiprazole and cariprazine on cholesterol biosynthesis. We report that cariprazine affects levels of 7-DHC and cholesterol in cell culture incubations at concentrations as low as 5 nM. Furthermore, a common metabolite of cariprazine and aripiprazole, 2,3-(dichlorophenyl) piperazine, inhibits DHCR7 activity at concentrations comparable to those of the potent teratogen AY9944. The cell culture experiments were corroborated in mice in studies showing that treatment with cariprazine elevated 7-DHC in brain and serum. The consequences of sterol inhibition by antipsychotics in the developing nervous system and the safety of their use during pregnancy remains to be established.

Prevention of Retinal Degeneration in a Rat Model of Smith-Lemli-Opitz Syndrome

Smith-Lemli-Opitz Syndrome (SLOS) is a recessive human disease caused by defective cholesterol (CHOL) synthesis at the level of DHCR7 (7-dehydrocholesterol reductase), which normally catalyzes the conversion of 7-dehydrocholesterol (7DHC) to CHOL. Formation and abnormal accumulation of 7DHC and 7DHC-derived oxysterols occur in SLOS patients and in rats treated with the DHCR7 inhibitor AY9944. The rat SLOS model exhibits progressive and irreversible retinal dysfunction and degeneration, which is only partially ameliorated by dietary CHOL supplementation. We hypothesized that 7DHC-derived oxysterols are causally involved in this retinal degeneration, and that blocking or reducing their formation should minimize the phenotype. Here, using the SLOS rat model, we demonstrate that combined dietary supplementation with CHOL plus antioxidants (vitamins E and C, plus sodium selenite) provides better outcomes than dietary CHOL supplementation alone with regard to preservation of retinal structure and function and lowering 7DHC-derived oxysterol formation. These proof-of-principle findings provide a translational, pre-clinical framework for designing clinical trials using CHOL-antioxidant combination therapy as an improved therapeutic intervention over the current standard of care for the treatment of SLOS.

Effect of psychotropic drug treatment on sterol metabolism

Cholesterol metabolism is vital for brain function. Previous work in cultured cells has shown that a number of psychotropic drugs inhibit the activity of 7-dehydrocholesterol reductase (DHCR7), an enzyme that catalyzes the final steps in cholesterol biosynthesis. This leads to the accumulation of 7-dehydrocholesterol (7DHC), a molecule that gives rise to oxysterols, vitamin D, and atypical neurosteroids. We examined levels of cholesterol and the cholesterol precursors desmosterol, lanosterol, 7DHC and its isomer 8-dehydrocholesterol (8DHC), in blood samples of 123 psychiatric patients on various antipsychotic and antidepressant drugs, and 85 healthy controls, to see if the observations in cell lines hold true for patients as well. Three drugs, aripiprazole, haloperidol and trazodone increased circulating 7DHC and 8DHC levels, while five other drugs, clozapine, escitalopram/citalopram, lamotrigine, olanzapine, and risperidone, did not. Studies in rat brain verified that haloperidol dose-dependently increased 7DHC and 8DHC levels, while clozapine had no effect. We conclude that further studies should investigate the role of 7DHC and 8DHC metabolites, such as oxysterols, vitamin D, and atypical neurosteroids, in the deleterious and therapeutic effects of psychotropic drugs. Finally, we recommend that drugs that increase 7DHC levels should not be prescribed during pregnancy, as children born with DHCR7 deficiency have multiple congenital malformations.

Sterols and oxysterols in plasma from Smith-Lemli-Opitz syndrome patients

Smith-Lemli-Opitz syndrome (SLOS) is a severe autosomal recessive disorder resulting from defects in the cholesterol synthesising enzyme 7-dehydrocholesterol reductase (Δ⁷-sterol reductase, DHCR7, EC 1.3.1.21) leading to a build-up of the cholesterol precursor 7-dehydrocholesterol (7-DHC) in tissues and blood plasma. Although the underling enzyme deficiency associated with SLOS is clear there are likely to be multiple mechanisms responsible for SLOS pathology. In an effort to learn more of the aetiology of SLOS we have analysed plasma from SLOS patients to search for metabolites derived from 7-DHC which may be responsible for some of the pathology. We have identified a novel hydroxy-8-dehydrocholesterol, which is either 24- or 25-hydroxy-8-dehydrocholesterol and also the known metabolites 26-hydroxy-8-dehydrocholesterol, 4-hydroxy-7-dehydrocholesterol, 3β,5α-dihydroxycholest-7-en-6-one and 7α,8α-epoxycholesterol. None of these metabolites are detected in control plasma at quantifiable levels (0.5ng/mL).

Assessment of altered lipid homeostasis by HILIC-ion mobility-mass spectrometry-based lipidomics

Ion mobility-mass spectrometry (IM-MS) has proven to be a highly informative technique for the characterization of lipids from cells and tissues. We report the combination of hydrophilic-interaction liquid chromatography (HILIC) with traveling-wave IM-MS (TWIM-MS) for comprehensive lipidomics analysis. Main lipid categories such as glycerolipids, sphingolipids, and glycerophospholipids are separated on the basis of their lipid backbones in the IM dimension, whereas subclasses of each category are mostly separated on the basis of their headgroups in the HILIC dimension, demonstrating the orthogonality of HILIC and IM separations. Using our previously established lipid calibrants for collision cross-section (CCS) measurements in TWIM, we measured over 250 CCS values covering 12 lipid classes in positive and negative modes. The coverage of the HILIC-IM-MS method is demonstrated in the analysis of Neuro2a neuroblastoma cells exposed to benzalkonium chlorides (BACs) with C10 or C16 alkyl chains, which we have previously shown to affect gene expression related to cholesterol and lipid homeostasis. We found that BAC exposure resulted in significant changes to several lipid classes, including glycerides, sphingomyelins, phosphatidylcholines, and phosphatidylethanolamines. Our results indicate that BAC exposure modifies lipid homeostasis in a manner that is dependent upon the length of the BAC alkyl chain.

Endogenous B-ring oxysterols inhibit the Hedgehog component Smoothened in a manner distinct from cyclopamine or side-chain oxysterols

Cellular lipids are speculated to act as key intermediates in Hedgehog signal transduction, but their precise identity and function remain enigmatic. In an effort to identify such lipids, we pursued a Hedgehog pathway inhibitory activity that is particularly abundant in flagellar lipids of Chlamydomonas reinhardtii, resulting in the purification and identification of ergosterol endoperoxide, a B-ring oxysterol. A mammalian analog of ergosterol, 7-dehydrocholesterol (7-DHC), accumulates in Smith-Lemli-Opitz syndrome, a human genetic disease that phenocopies deficient Hedgehog signaling and is caused by genetic loss of 7-DHC reductase. We found that depleting endogenous 7-DHC with methyl-β-cyclodextrin treatment enhances Hedgehog activation by a pathway agonist. Conversely, exogenous addition of 3β,5α-dihydroxycholest-7-en-6-one, a naturally occurring B-ring oxysterol derived from 7-DHC that also accumulates in Smith-Lemli-Opitz syndrome, blocked Hedgehog signaling by inhibiting activation of the essential transduction component Smoothened, through a mechanism distinct from Smoothened modulation by other lipids.

Inhibitors of 7-Dehydrocholesterol Reductase: Screening of a Collection of Pharmacologically Active Compounds in Neuro2a Cells

A small library of pharmacologically active compounds (the NIH Clinical Collection) was assayed in Neuro2a cells to determine their effect on the last step in the biosynthesis of cholesterol, the transformation of 7-dehydrocholesterol (7-DHC) to cholesterol promoted by 7-dehydrocholesterol reductase, DHCR7. Of some 727 compounds in the NIH Clinical Collection, over 30 compounds significantly increased 7-DHC in Neuro2a cells when assayed at 1 μM. Active compounds that increased 7-DHC with a Z-score of +3 or greater generally gave rise to modest decreases in desmosterol and increases in lanosterol levels. Among the most active compounds identified in the library were the antipsychotic, antidepressant, and anxiolytic compounds that included perospirone, nefazodone, haloperidol, aripiprazole, trazodone, and buspirone. Fluoxetine and risperidone were also active at 1 μM, and another 10 compounds in this class of pharmaceuticals were identified in the screen at concentrations of 10 μM. Increased levels of 7-DHC are associated with Smith-Lemli-Opitz syndrome (SLOS), a human condition that results from a mutation in the gene that encodes DHCR7. The SLOS phenotype includes neurological deficits and congenital malformations, and it is linked to a higher incidence of autism spectrum disorder. The significance of the current study is that it identifies common pharmacological compounds that may induce a biochemical presentation similar to SLOS. Little is known about the side effects of elevated 7-DHC postdevelopmentally, and the elevated 7-DHC that results from exposure to these compounds may also be a confounder in the diagnosis of SLOS.

Differential cytotoxic effects of 7-dehydrocholesterol-derived oxysterols on cultured retina-derived cells: Dependence on sterol structure, cell type, and density

Tissue accumulation of 7-dehydrocholesterol (7DHC) is a hallmark of Smith-Lemli-Opitz Syndrome (SLOS), a human inborn error of the cholesterol (CHOL) synthesis pathway. Retinal 7DHC-derived oxysterol formation occurs in the AY9944-induced rat model of SLOS, which exhibits a retinal degeneration characterized by selective loss of photoreceptors and associated functional deficits, Müller cell hypertrophy, and engorgement of the retinal pigment epithelium (RPE) with phagocytic inclusions. We evaluated the relative effects of four 7DHC-derived oxysterols on three retina-derived cell types in culture, with respect to changes in cellular morphology and viability. 661W (photoreceptor-derived) cells, rMC-1 (Müller glia-derived) cells, and normal diploid monkey RPE (mRPE) cells were incubated for 24 h with dose ranges of either 7-ketocholesterol (7kCHOL), 5,9-endoperoxy-cholest-7-en-3β,6α-diol (EPCD), 3β,5α-dihydroxycholest-7-en-6-one (DHCEO), or 4β-hydroxy-7-dehydrocholesterol (4HDHC); CHOL served as a negative control (same dose range), along with appropriate vehicle controls, while staurosporine (Stsp) was used as a positive cytotoxic control. For 661W cells, the rank order of oxysterol potency was: EPCD > 7kCHOL >> DHCEO > 4HDHC ≈ CHOL. EC50 values were higher for confluent vs. subconfluent cultures. 661W cells exhibited much higher sensitivity to EPCD and 7kCHOL than either rMC-1 or mRPE cells, with the latter being the most robust when challenged, either at confluence or in sub-confluent cultures. When tested on rMC-1 and mRPE cells, EPCD was again an order of magnitude more potent than 7kCHOL in compromising cellular viability. Hence, 7DHC-derived oxysterols elicit differential cytotoxicity that is dose-, cell type-, and cell density-dependent. These results are consistent with the observed progressive, photoreceptor-specific retinal degeneration in the rat SLOS model, and support the hypothesis that 7DHC-derived oxysterols are causally linked to that retinal degeneration as well as to SLOS.

Identification of Environmental Quaternary Ammonium Compounds as Direct Inhibitors of Cholesterol Biosynthesis

In this study, we aim to identify environmental molecules that can inhibit cholesterol biosynthesis, potentially leading to the same biochemical defects as observed in cholesterol biosynthesis disorders, which are often characterized by congenital malformations and developmental delay. Using the Distributed Structure-Searchable Toxicity (DSSTox) Database Network developed by EPA, we first carried out in silico screening of environmental molecules that display structures similar to AY9944, a known potent inhibitor of 3β-hydroxysterol-Δ(7)-reductase (DHCR7)-the last step of cholesterol biosynthesis. Molecules that display high similarity to AY9944 were subjected to test in mouse and human neuroblastoma cells for their effectiveness in inhibiting cholesterol biosynthesis by analyzing cholesterol and its precursor using gas chromatography-mass spectrometry. We found that a common disinfectant mixture, benzalkonium chlorides (BACs), exhibits high potency in inhibiting DHCR7, as suggested by greatly elevated levels of the cholesterol precursor, 7-dehydrocholesterol (7-DHC). Subsequent structure-activity studies suggested that the potency of BACs as Dhcr7 inhibitors decrease with the length of their hydrocarbon chain: C10 > C12 ≫ C14 > C16. Real-time qPCR analysis revealed upregulation of the genes related to cholesterol biosynthesis and downregulation of the genes related to cholesterol efflux, suggesting a feedback response to the inhibition. Furthermore, an oxidative metabolite of 7-DHC that was previously identified as a biomarker in vivo was also found in cells exposed to BACs by liquid chromatography-mass spectrometry. Our findings suggest that certain environmental molecules could potently inhibit cholesterol biosynthesis, which could be a new link between environment and developmental disorders.

The Effect of Small Molecules on Sterol Homeostasis: Measuring 7-Dehydrocholesterol in Dhcr7-Deficient Neuro2a Cells and Human Fibroblasts

Well-established cell culture models were combined with new analytical methods to assess the effects of small molecules on the cholesterol biosynthesis pathway. The analytical protocol, which is based on sterol derivation with the dienolphile PTAD, was found to be reliable for the analysis of 7-DHC and desmosterol. The PTAD method was applied to the screening of a small library of pharmacologically active substances, and the effect of compounds on the cholesterol pathway was determined. Of some 727 compounds, over 30 compounds decreased 7-DHC in Dhcr7-deficient Neuro2a cells. The examination of chemical structures of active molecules in the screen grouped the compounds into distinct categories. In addition to statins, our screen found that SERMs, antifungals, and several antipsychotic medications reduced levels of 7-DHC. The activities of selected compounds were verified in human fibroblasts derived from Smith-Lemli-Opitz syndrome (SLOS) patients and linked to specific transformations in the cholesterol biosynthesis pathway.

Free radical oxidation of cholesterol and its precursors: Implications in cholesterol biosynthesis disorders

Free radical oxidation of cholesterol and its precursors contribute significantly to the pathophysiology of a number of human diseases. This review intends to summarize recent developments and provide a perspective on the reactivities of sterols toward free radical oxidation, the free radical reaction mechanism, and the biological consequences of oxysterols derived from the highly oxidizable cholesterol precursor, 7-dehydrocholesterol. We propose that the rigid structures, additional substituents on the double bonds, and the well-aligned reactive C-H bonds in sterols make them more prone to free radical oxidation than their acyclic analogs found in unsaturated fatty acids. The mechanism of sterol peroxidation follows some well-established reaction pathways found in the free radical peroxidation of polyunsaturated fatty acids, but sterols also undergo some reactions that are unique to these compounds. Peroxidation of 7-dehydrocholesterol gives arguably the most diverse set of oxysterol products that have been observed to date. The metabolism of these oxysterols in cells and the biological consequences of their formation will be discussed in the context of the pathophysiology of the human disease Smith-Lemli-Opitz syndrome. Considering the high reactivity of sterols, we propose that a number of other cholesterol biosynthesis disorders may be associated with oxidative stress.

Oxidation of 7-dehydrocholesterol and desmosterol by human cytochrome P450 46A1

Cytochrome P450 (P450 or CYP) 46A1 is expressed in brain and has been characterized by its ability to oxidize cholesterol to 24S-hydroxycholesterol. In addition, the same enzyme is known to further oxidize 24S-hydroxycholesterol to the 24,25- and 24,27-dihydroxy products, as well as to catalyze side-chain oxidations of 7α-hydroxycholesterol and cholestanol. As precursors in the biosynthesis of cholesterol, 7-dehydrocholesterol has not been found to be a substrate of P450 46A1 and desmosterol has not been previously tested. However, 24-hydroxy-7-dehydrocholesterol was recently identified in brain tissues, which prompted us to reexamine this enzyme and its potential substrates. Here we report that P450 46A1 oxidizes 7-dehydrocholesterol to 24-hydroxy-7-dehydrocholesterol and 25-hydroxy-7-dehydrocholesterol, as confirmed by LC-MS and GC-MS. Overall, the catalytic rates of formation increased in the order of 24-hydroxy-7-dehydrocholesterol < 24-hydroxycholesterol < 25-hydroxy-7-dehydrocholesterol from their respective precursors, with a ratio of 1:2.5:5. In the case of desmosterol, epoxidation to 24S,25-epoxycholesterol and 27-hydroxylation was observed, at roughly equal rates. The formation of these oxysterols in the brain may be of relevance in Smith-Lemli-Opitz syndrome, desmosterolosis, and other relevant diseases, as well as in signal transduction by lipids.

Recent advances in cholesterol chemistry

This review article presents advances in cholesterol chemistry since 2000. Various transformations (chemical, enzymatic, electrochemical, etc.) of cholesterol are presented. A special emphasis is given to cholesterol oxidation reactions, but also substitution of the 3β-hydroxyl group, addition to the C5-C6 double bond, C-H functionalization, and C-C bond forming reactions are discussed.

Cholesterol in the retina: the best is yet to come

Historically understudied, cholesterol in the retina is receiving more attention now because of genetic studies showing that several cholesterol-related genes are risk factors for age-related macular degeneration (AMD) and because of eye pathology studies showing high cholesterol content of drusen, aging Bruch's membrane, and newly found subretinal lesions. The challenge before us is determining how the cholesterol-AMD link is realized. Meeting this challenge will require an excellent understanding these genes' roles in retinal physiology and how chorioretinal cholesterol is maintained. In the first half of this review, we will succinctly summarize physico-chemical properties of cholesterol, its distribution in the human body, general principles of maintenance and metabolism, and differences in cholesterol handling in human and mouse that impact on experimental approaches. This information will provide a backdrop to the second part of the review focusing on unique aspects of chorioretinal cholesterol homeostasis, aging in Bruch's membrane, cholesterol in AMD lesions, a model for lesion biogenesis, a model for macular vulnerability based on vascular biology, and alignment of AMD-related genes and pathobiology using cholesterol and an atherosclerosis-like progression as unifying features. We conclude with recommendations for the most important research steps we can take towards delineating the cholesterol-AMD link.

Liver transplantation in defects of cholesterol biosynthesis: the case of lathosterolosis

We report the outcome of liver transplantation (LT) in the only surviving patient with lathosterolosis, a defect of cholesterol biosynthesis characterized by high lathosterol levels associated with progressive cholestasis, multiple congenital anomalies and mental retardation. From her diagnosis at age 2 she had shown autistic behavior, was unable to walk unaided and her sight was impaired by cataracts. By age 7 she developed end-stage liver disease. After a soul-searching discussion within the transplantation team, she was treated with LT as this represented her only lifesaving option. At 1-year follow-up, her lathosterol levels had returned to normal (0.61 mg/dL from 13.04 ± 2.65) and her nutrition improved. She began exploring her environment and walking by holding onto an adult's hand and then independently. Her brain magnetic resonance imaging (MRI) had shown a normal picture at age 1, whereas a volume reduction of white matter with ex vacuo ventricular dilatation and defective myelinization were observed before transplant. At 5-year follow-up, a complete biochemical recovery, an arrest of mental deterioration and a stable MRI picture were achieved, with a return to her every day life albeit with limitations. Timely liver transplant in defects of cholesterol biosynthesis might arrest the progression of neurological damage.

Antioxidant supplementation ameliorates molecular deficits in Smith-Lemli-Opitz syndrome

BACKGROUND

Smith-Lemli-Opitz syndrome (SLOS) is an inborn error of cholesterol biosynthesis characterized by diminished cholesterol and increased 7-dehydrocholesterol (7-DHC) levels. 7-Dehydrocholesterol is highly reactive, giving rise to biologically active oxysterols.

METHODS

7-DHC-derived oxysterols were measured in fibroblasts from SLOS patients and an in vivo SLOS rodent model using high-performance liquid chromatography tandem mass spectrometry. Expression of lipid biosynthesis genes was ascertained by quantitative polymerase chain reaction and Western blot. The effects of an antioxidant mixture of vitamin A, coenzyme Q10, vitamin C, and vitamin E were evaluated for their potential to reduce formation of 7-DHC oxysterols in fibroblast from SLOS patients. Finally, the effect of maternal feeding of vitamin E enriched diet was ascertained in the brain and liver of newborn SLOS mice.

RESULTS

In cultured human SLOS fibroblasts, the antioxidant mixture led to decreased levels of the 7-DHC-derived oxysterol, 3β,5α-dihydroxycholest-7-en-6-one. Furthermore, gene expression changes in SLOS human fibroblasts were normalized with antioxidant treatment. The active ingredient appeared to be vitamin E, as even at low concentrations, it significantly decreased 3β,5α-dihydroxycholest-7-en-6-one levels. In addition, analyzing a mouse SLOS model revealed that feeding a vitamin E enriched diet to pregnant female mice led to a decrease in oxysterol formation in brain and liver tissues of the newborn Dhcr7-knockout pups.

CONCLUSIONS

Considering the adverse effects of 7-DHC-derived oxysterols in neuronal and glial cultures and the positive effects of antioxidants in patient cell cultures and the transgenic mouse model, we believe that preventing formation of 7-DHC oxysterols is critical for countering the detrimental effects of DHCR7 mutations.

Elevated Autophagy and Mitochondrial Dysfunction in the Smith-Lemli-Opitz Syndrome

Smith–Lemli–Opitz Syndrome (SLOS) is a congenital, autosomal recessive metabolic and developmental disorder caused by mutations in the enzyme which catalyzes the reduction of 7-dehydrocholesterol (7DHC) to cholesterol. Herein we show that dermal fibroblasts obtained from SLOS children display increased basal levels of LC3B-II, the hallmark protein signifying increased autophagy. The elevated LC3B-II is accompanied by increased beclin-1 and cellular autophagosome content. We also show that the LC3B-II concentration in SLOS cells is directly proportional to the cellular concentration of 7DHC, suggesting that the increased autophagy is caused by 7DHC accumulation secondary to defective DHCR7. Further, the increased basal LC3B-II levels were decreased significantly by pretreating the cells with antioxidants implicating a role for oxidative stress in elevating autophagy in SLOS cells. Considering the possible source of oxidative stress, we examined mitochondrial function in the SLOS cells using JC-1 assay and found significant mitochondrial dysfunction compared to mitochondria in control cells. In addition, the levels of PINK1 which targets dysfunctional mitochondria for removal by the autophagic pathway are elevated in SLOS cells, consistent with mitochondrial dysfunction as a stimulant of mitophagy in SLOS. This suggests that the increase in autophagic activity may be protective, i.e., to remove dysfunctional mitochondria. Taken together, these studies are consistent with a role for mitochondrial dysfunction leading to increased autophagy in SLOS pathophysiology.