Tamoxifen is a potent inhibitor of cholesterol esterification and prevents the formation of foam cells

Reversible translocation of acyl-CoA:cholesterol acyltransferase (ACAT) between the endoplasmic reticulum and vesicular structures

The enzyme acyl-CoA:cholesterol acyltransferase (ACAT) is normally localized in the endoplasmic reticulum (ER) where it can esterify cholesterol for storage in lipid droplets and/or the formation of lipoproteins. Here, we report that ACAT can translocate from the ER into vesicular structures in response to different ACAT inhibitors. The translocation was fast (within minutes), reversible and occurred in different cell types. Interestingly, oleic acid was able to fasten the re-translocation from vesicles back into the reticular ER network. The process of ACAT translocation could also be induced by cyclodextrins, cholesterol, lanosterol (but not 4-cholestene-3 one), 25-hydroxycholesterol, and by certain stress stimuli such as hyperosmolarity (sucrose treatment), temperature change, or high-density cultivation. In vitro esterification showed that ACAT remains fully active after it has been translocated to vesicles in response to hyperosmotic sucrose treatment of the cells. The translocation process was not accompanied by changes in the electrophoretic mobility of ACAT, even after chemical crosslinking. Interestingly, the protein synthesis inhibitor cycloheximide showed a stimulating effect on ACAT activity and prevented the translocation of ACAT from the ER into vesicles.

Chemical synthesis and biochemical properties of cholestane-5α,6β-diol-3-sulfonate: A non-hydrolysable analogue of cholestane-5α,6β-diol-3β-sulfate

Cholestane-3β,5α,6β-triol (CT) is a primary metabolite of 5,6-epoxycholesterols (5,6-EC) that is catalyzed by the cholesterol-5,6-epoxide hydrolase (ChEH). CT is a well-known biomarker for Niemann-Pick disease type C (NP-C), a progressive inherited neurodegenerative disease. On the other hand, CT is known to be metabolized by the 11β-hydroxysteroid-dehydrogenase of type 2 (11β-HSD2) into a tumor promoter named oncosterone that stimulates the growth of breast cancer tumors. Sulfation is a major metabolic transformation leading to the production of sulfated oxysterols. The production of cholestane-5α,6β-diol-3β-O-sulfate (CDS) has been reported in breast cancer cells. However, no data related to CDS biological properties have been reported so far. These studies have been hampered because sulfate esters of sterols and steroids are rapidly hydrolyzed by steroid sulfatase to give free steroids and sterols. In order to get insight into the biological properties of CDS, we report herein the synthesis and the characterization of cholestane-5α,6β-diol-3β-sulfonate (CDSN), a non-hydrolysable analogue of CDS. We show that CDSN is a potent inhibitor of 11β-HSD2 that blocks oncosterone production on cell lysate. The inhibition of oncosterone biosynthesis of a whole cell assay was observed but results from the blockage by CDSN of the uptake of CT in MCF-7 cells. While CDSN inhibits MCF-7 cell proliferation, we found that it potentiates the cytotoxic activity of post-lanosterol cholesterol biosynthesis inhibitors such as tamoxifen and PBPE. This effect was associated with an increase of free sterols accumulation and the appearance of giant multilamellar bodies, a structural feature reminiscent of Type C Niemann-Pick disease cells and consistent with a possible inhibition by CDSN of NPC1. Altogether, our data showed that CDSN is biologically active and that it is a valuable tool to study the biological properties of CDS and more specifically its impact on immunity and viral infection.

Confounding Effects of Tamoxifen: Cautionary and Practical Considerations for the Use of Tamoxifen-Inducible Mouse Models in Atherosclerosis Research-Brief Report

BACKGROUND

In recent years, fate-mapping lineage studies in mouse models have led to major advances in vascular biology by allowing investigators to track specific cell populations in vivo. One of the most frequently used lineage tracing approaches involves tamoxifen-inducible CreERT-LoxP systems. However, tamoxifen treatment can also promote effects independent of Cre recombinase activation, many of which have not been fully explored.

METHODS

To elucidate off-target effects of tamoxifen, male and female mice were either unmanipulated or injected with tamoxifen or corn oil. All mice received PCSK9 (proprotein convertase subtilisin/kexin type 9)-AAV (adeno-associated virus) injections and a modified Western diet to induce hypercholesterolemia. After 2 weeks, serum cholesterol and liver morphology were assessed. To determine the duration of any tamoxifen effects in long-term atherosclerosis experiments, mice received either 12 days of tamoxifen at baseline or 12 days plus 2 sets of 5-day tamoxifen boosters; all mice received PCSK9-AAV injections and a modified Western diet to induce hypercholesterolemia. After 24 weeks, serum cholesterol and aortic sinus plaque burden were measured.

RESULTS

After 2 weeks of atherogenic treatment, mice injected with tamoxifen demonstrated significantly reduced serum cholesterol levels compared with uninjected- or corn oil-treated mice. However, there were no differences in PCSK9-mediated knockdown of LDL (low-density lipoprotein) receptors between the groups. Additionally, tamoxifen-treated mice exhibited significantly increased hepatic lipid accumulation compared with the other groups. Finally, the effects of tamoxifen remained for at least 8 weeks after completion of injections, with mice demonstrating persistent decreased serum cholesterol and impaired atherosclerotic plaque formation.

CONCLUSIONS

In this study, we establish that tamoxifen administration results in decreased serum cholesterol, decreased plaque formation, and increased hepatic lipid accumulation. These alterations represent significant confounding variables in atherosclerosis research, and we urge future investigators to take these findings into consideration when planning and executing their own atherosclerosis experiments.

The beneficial effects of tamoxifen on arteries: a key player for cardiovascular health of breast cancer patient

Breast cancer is the most common cancer in women. Over the past few decades, advances in cancer detection and treatment have significantly improved survival rate of breast cancer patients. However, due to the cardiovascular toxicity of cancer treatments (chemotherapy, anti-HER2 antibodies and radiotherapy), cardiovascular diseases (CVD) have become an increasingly important cause of long-term morbidity and mortality in breast cancer survivors. Endocrine therapies are prescribed to reduce the risk of recurrence and specific death in estrogen receptor-positive (ER+) early breast cancer patients, but their impact on CVD is a matter of debate. Whereas aromatase inhibitors and luteinizing hormone-releasing hormone (LHRH) analogs inhibit estrogen synthesis, tamoxifen acts as a selective estrogen receptor modulator (SERM), opposing estrogen action in the breast but mimicking their actions in other tissues, including arteries. This review aims to summarize the main clinical and experimental studies reporting the effects of tamoxifen on CVD. In addition, we will discuss how recent findings on the mechanisms of action of these therapies may contribute to a better understanding and anticipation of CVD risk in breast cancer patients.

Association of circulating free and total oxysterols in breast cancer patients

OBJECTIVES

Oxysterols, a family of oxidized cholesterol derivates, are of increasing interest due to their role in cancer development and progression. Some oxysterols are estrogen receptor modulators and thus of particular interest in breast cancer research. In human studies, two forms of circulating oxysterols are commonly evaluated: "free" (unesterified) and "total" (esterified and unesterified). However, associations between free and total oxysterols are not well established. We addressed this knowledge gap in a pilot study by evaluating correlations between the free and the total form of each of the circulating oxysterols (free vs. total), and pairwise associations within the panel of total oxysterols (total vs. total) and the panel of free oxysterols (free vs. free).

METHODS

Concentrations of oxysterols and other non-cholesterol sterols were quantified in blood samples of 27 breast cancer patients from the MARIE breast cancer patient cohort using liquid chromatography mass spectrometry. We used Spearman rank correlations to assess associations. Overall, 12 oxysterols (including 27-hydroxycholesterol (HC), 25-HC, 24S-HC, 7a-HC, 5a6a-epoxycholesterol) and five sterols (including lanosterol and desmosterol) were analyzed.

RESULTS

Strong correlations (r≥0.82) were observed for seven circulating free and total oxysterols/sterols. The free and total form of 27-HC (r=0.63), 25-HC (r=0.54), and two more oxysterols were weaker correlated. Correlation patterns in the panel of total oxysterols/sterols and the panel of free oxysterols/sterols were similar.

CONCLUSIONS

These findings demonstrate that concentrations of most free and total oxysterols/sterols are strongly correlated. We provide further insight into the interrelationships between oxysterols in breast cancer patients.

The Liver X Receptor Is Selectively Modulated to Differentially Alter Female Mammary Metastasis-associated Myeloid Cells

Dysregulation of cholesterol homeostasis is associated with many diseases such as cardiovascular disease and cancer. Liver X receptors (LXRs) are major upstream regulators of cholesterol homeostasis and are activated by endogenous cholesterol metabolites such as 27-hydroxycholesterol (27HC). LXRs and various LXR ligands such as 27HC have been described to influence several extra-hepatic biological systems. However, disparate reports of LXR function have emerged, especially with respect to immunology and cancer biology. This would suggest that, similar to steroid nuclear receptors, the LXRs can be selectively modulated by different ligands. Here, we use RNA-sequencing of macrophages and single-cell RNA-sequencing of immune cells from metastasis-bearing murine lungs to provide evidence that LXR satisfies the 2 principles of selective nuclear receptor modulation: (1) different LXR ligands result in overlapping but distinct gene expression profiles within the same cell type, and (2) the same LXR ligands differentially regulate gene expression in a highly context-specific manner, depending on the cell or tissue type. The concept that the LXRs can be selectively modulated provides the foundation for developing precision pharmacology LXR ligands that are tailored to promote those activities that are desirable (proimmune), but at the same time minimizing harmful side effects (such as elevated triglyceride levels).

Tamoxifen treatment ameliorates contractile dysfunction of Duchenne muscular dystrophy stem cell-derived cardiomyocytes on bioengineered substrates

Duchenne muscular dystrophy (DMD) is a progressive genetic myopathy that leads to heart failure from dilated cardiomyopathy by early adulthood. Recent evidence suggests that tamoxifen, a selective estrogen receptor modulator widely used to treat breast cancer, ameliorates DMD cardiomyopathy. However, the mechanism of action of 4-hydroxytamoxifen, the active metabolite of tamoxifen, on cardiomyocyte function remains unclear. To examine the effects of chronic 4-hydroxytamoxifen treatment, we used state-of-the-art human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) and a bioengineered platform to model DMD. We assessed the beating rate and beating velocity of iPSC-CMs in monolayers and as single cells on micropatterns that promote a physiological cardiomyocyte morphology. We found that 4-hydroxytamoxifen treatment of DMD iPSC-CMs decreased beating rate, increased beating velocity, and ameliorated calcium-handling deficits, leading to prolonged viability. Our study highlights the utility of a bioengineered iPSC-CM platform for drug testing and underscores the potential of repurposing tamoxifen as a therapy for DMD cardiomyopathy.

Cell cycle dependence on the mevalonate pathway: Role of cholesterol and non-sterol isoprenoids

The mevalonate pathway is responsible for the synthesis of isoprenoids, including sterols and other metabolites that are essential for diverse biological functions. Cholesterol, the main sterol in mammals, and non-sterol isoprenoids are in high demand by rapidly dividing cells. As evidence of its importance, many cell signaling pathways converge on the mevalonate pathway and these include those involved in proliferation, tumor-promotion, and tumor-suppression. As well as being a fundamental building block of cell membranes, cholesterol plays a key role in maintaining their lipid organization and biophysical properties, and it is crucial for the function of proteins located in the plasma membrane. Importantly, cholesterol and other mevalonate derivatives are essential for cell cycle progression, and their deficiency blocks different steps in the cycle. Furthermore, the accumulation of non-isoprenoid mevalonate derivatives can cause DNA replication stress. Identification of the mechanisms underlying the effects of cholesterol and other mevalonate derivatives on cell cycle progression may be useful in the search for new inhibitors, or the repurposing of preexisting cholesterol biosynthesis inhibitors to target cancer cell division. In this review, we discuss the dependence of cell division on an active mevalonate pathway and the role of different mevalonate derivatives in cell cycle progression.

The role of MYB proto-oncogene like 2 in tamoxifen resistance in breast cancer

Despite the efficacy of tamoxifen in preventing disease relapse, a large portion of breast cancer patients show intrinsic or acquired resistance to tamoxifen, leading to treatment failure and unfavorable clinical outcome. MYB proto-oncogene like 2 (MYBL2) is a transcription factor implicated in the initiation and progression of various human cancers. However, its role in tamoxifen resistance in breast cancer remained largely unknown. In the present study, by analyzing public transcriptome dataset, we found that MYBL2 is overexpressed in breast cancer and is associated with the poor prognosis of breast cancer patients. By establishing tamoxifen-resistant breast cancer cell lines, we also provided evidence that MYBL2 overexpression contributes to tamoxifen resistance by up-regulating its downstream transcriptional effectors involved in cell proliferation (PLK1, PRC1), survival (BIRC5) and metastasis (HMMR). In contrast, inhibiting those genes via MYBL2 depletion suppresses cancer progression, restores tamoxifen and eventually reduces the risk of disease recurrence. All these findings revealed a critical role of MYBL2 in promoting tamoxifen resistance and exacerbating the progression of breast cancer, which may serve as a novel therapeutic target to overcome drug resistance and improve the prognosis of breast cancer patients.

Role of cholesterol metabolism in the anticancer pharmacology of selective estrogen receptor modulators

Selective estrogen receptor modulators (SERMs) are a class of compounds that bind to estrogen receptors (ERs) and possess estrogen agonist or antagonist actions in different tissues. As such, they are widely used drugs. For instance, tamoxifen, the most prescribed SERM, is used to treat ERα-positive breast cancer. Aside from their therapeutic targets, SERMs have the capacity to broadly affect cellular cholesterol metabolism and handling, mainly through ER-independent mechanisms. Cholesterol metabolism reprogramming is crucial to meet the needs of cancer cells, and different key processes involved in cholesterol homeostasis have been associated with cancer progression. Therefore, the effects of SERMs on cholesterol homeostasis may be relevant to carcinogenesis, either by contributing to the anticancer efficacy of these compounds or, conversely, by promoting resistance to treatment. Understanding these aspects of SERMs actions could help to design more efficacious therapies. Herein we review the effects of SERMs on cellular cholesterol metabolism and handling and discuss their potential in anticancer pharmacology.

The effect of bergamot polyphenolic fraction on lipid transfer protein system and vascular oxidative stress in a rat model of hyperlipemia

BACKGROUND

Experimental and epidemiological studies show that bergamot polyphenolic fraction (BPF) ameliorates the serum lipemic profile, normalizes blood pressure and improves non alcoholic fatty liver disease in patients suffering from metabolic syndrome. Despite this evidence, the molecular mechanisms responsible for these beneficial effects remain unclear. The aim of our study is to clarify the effects of BPF on the lipoprotein assembly and to identify oxidative stress biomarkers correlating hyperlipidaemia and BPF-induced metabolic changes.

METHODS

Male Wistar rats (180-200 g) were randomly assigned to receive a standard diet, a hypercholesterolemic diet or a hypercholesterolemic diet+BPF (20 mg/Kg/rat daily, gavage), respectively, for 90 days. Total cholesterol (tChol), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), triglycerides (TG) and fasting plasma glucose were evaluated at the baseline as well as at the end of the treatment. To assess the effect of BPF on the Lipid Transfer Protein System, detection of ACAT, LCAT, CETP, PON1, Apo A1 and Apo B have also been carried out. Finally, the lipid peroxidation biomarker (TBARS) and oxyLDL were also measured.

RESULTS

BPF prevented tChol, LDL-C, TG and fasting plasma glucose enhancement and improved HDL-C. Treatment of hyperlipæmic rats with BPF significantly restored altered the serum concentration of lipemic biomarkers and the activity of ACAT, LCAT, CETP and PON1, an effect accompanied by the concomitant normalization of Apo A1 and APO B levels. In addition, TBARS levels were reduced significantly by the treatment with BPF.

CONCLUSIONS

BPF prevents diet-induced alteration of the lipid profile in rats, counteracting oxidative stress and improving the dysregulation of the Lipid Transfer Protein System. These data add new insights into the molecular mechanisms underlying the beneficial role of BPF in the therapy of hyperlipidaemia, thus suggesting a novel approach in the prevention of cardiovascular disease.

Therapeutic effects of tamoxifen on metabolic parameters and cytokines modulation in rat model of postmenopausal diabetic cardiovascular dysfunction: Role of classic estrogen receptors

In postmenopausal women, the risk of diabetic cardiovascular disease drastically increases compared with that of premenopausal women. In the present study we surveyed the effects of Tamoxifen (TAM) and 17-β-estradiol (E2) on diabetic cardiovascular dysfunction. Female wistar rats were divided into six groups: sham-control, Diabetes, Ovariectomized (OVX) + Diabetes, OVX + Diabetes + Vehicle, OVX + Diabetes + E2, OVX + Diabetes + TAM. Type 2 diabetes was induced by High Fat Diet and low doses of STZ. E2 and TAM were administrated every four days for four weeks. Results show that, TAM or E2 reduces cardiac weight, atherogenic and cardiac risk indices. Mean arterial blood pressure (MABP) increased in diabetes group, while TAM and E2 prevented MABP increment. Also, fasting blood glucose was decreased by TAM and E2. Significant decrement in the level of IL-10 was observed in diabetes group and this effect was abolished by TAM and E2. Also, treatment with TAM and E2 resulted in improved inflammatory balance in favor of anti-inflammation. Although diabetes resulted in, increment of TC and LDL, TAM and E2 reduced lipids profile. Furthermore, treatment with TAM prevented the reduction of estrogen receptors (ERs) α and β protein levels, but its effect on the ERβ protein level was higher. Our results indicated that TAM protects against diabetic cardiovascular dysfunction and is a good candidate for E2 substitution.

Multimodal gadolinium oxysulfide nanoparticles: a versatile contrast agent for mesenchymal stem cell labeling

Despite a clear development of innovative therapies based on stem cell manipulation, the availability of new tools to better understand and follow stem cell behavior and improve their biomedical applications is not adequate. Indeed, an ideal tracking device must have good ability to label stem cells as well as complete neutrality relative to their biology. Furthermore, preclinical studies imply in vitro and in vivo approaches that often require several kinds of labeling and/or detection procedures. Consequently, the multimodality concept presented in this work may present a solution to this problem as it has the potential to combine complementary imaging techniques. Spherical europium-doped gadolinium oxysulfide (Gd2O2S:Eu3+) nanoparticles are presented as a candidate as they are detectable by (1) magnetic resonance (MRI), (2) X-ray and (3) photoluminescence imaging. Whole body in vivo distribution, elimination and toxicity evaluation revealed a high tolerance of nanoparticles with a long-lasting MRI signal and slow hepatobiliary and renal clearance. In vitro labeling of a wide variety of cells unveils the nanoparticle potential for efficient and universal cell tracking. Emphasis on mesenchymal stromal cells (MSCs) leads to the definition of optimal conditions for labeling and tracking in the context of cell therapy: concentrations below 50 μg mL-1 and diameters between 170 and 300 nm. Viability, proliferation, migration and differentiation towards mesodermal lineages are preserved under these conditions, and cell labeling appears to be persistent and without any leakage. Ex vivo detection of as few as five thousand Gd2O2S:Eu3+-labeled MSCs by MRI combined with in vitro examination with fluorescence microscopy highlights the feasibility of cell tracking in cell therapy using this new nanoplatform.

Bryonolic Acid Blocks Cancer Cell Clonogenicity and Invasiveness through the Inhibition of Fatty Acid: Cholesteryl Ester Formation

Bryonolic acid (BrA) is a pentacyclic triterpene present in several plants used in African traditional medicine such as Anisophyllea dichostyla R. Br. Here we investigated the in vitro anticancer properties of BrA. We report that BrA inhibits acyl-coA: cholesterol acyl transferase (ACAT) activity in rat liver microsomes in a concentration-dependent manner, blocking the biosynthesis of the cholesterol fatty acid ester tumour promoter. We next demonstrated that BrA inhibits ACAT in intact cancer cells with an IC₅₀ of 12.6 ± 2.4 µM. BrA inhibited both clonogenicity and invasiveness of several cancer cell lines, establishing that BrA displays specific anticancer properties. BrA appears to be more potent than the other pentacyclic triterpenes, betulinic acid and ursolic acid studied under similar conditions. The inhibitory effect of BrA was reversed by exogenous addition of cholesteryl oleate, showing that ACAT inhibition is responsible for the anticancer effect of BrA. This report reveals new anticancer properties for BrA.

Clinically used selective estrogen receptor modulators affect different steps of macrophage-specific reverse cholesterol transport

Selective estrogen receptor modulators (SERMs) are widely prescribed drugs that alter cellular and whole-body cholesterol homeostasis. Here we evaluate the effect of SERMs on the macrophage-specific reverse cholesterol transport (M-RCT) pathway, which is mediated by HDL. Treatment of human and mouse macrophages with tamoxifen, raloxifene or toremifene induced the accumulation of cytoplasmic vesicles of acetyl-LDL-derived free cholesterol. The SERMs impaired cholesterol efflux to apolipoprotein A-I and HDL, and lowered ABCA1 and ABCG1 expression. These effects were not altered by the antiestrogen ICI 182,780 nor were they reproduced by 17β-estradiol. The treatment of mice with tamoxifen or raloxifene accelerated HDL-cholesteryl ester catabolism, thereby reducing HDL-cholesterol concentrations in serum. When [³H]cholesterol-loaded macrophages were injected into mice intraperitoneally, tamoxifen, but not raloxifene, decreased the [³H]cholesterol levels in serum, liver and feces. Both SERMs downregulated liver ABCG5 and ABCG8 protein expression, but tamoxifen reduced the capacity of HDL and plasma to promote macrophage cholesterol efflux to a greater extent than raloxifene. We conclude that SERMs interfere with intracellular cholesterol trafficking and efflux from macrophages. Tamoxifen, but not raloxifene, impair M-RCT in vivo. This effect is primarily attributable to the tamoxifen-mediated reduction of the capacity of HDL to promote cholesterol mobilization from macrophages.

Design and synthesis of triarylacrylonitrile analogues of tamoxifen with improved binding selectivity to protein kinase C

The clinical selective estrogen receptor modulator tamoxifen is also a modest inhibitor of protein kinase C, a target implicated in several untreatable brain diseases such as amphetamine abuse. This inhibition and tamoxifen's ability to cross the blood brain barrier make it an attractive scaffold to conduct further SAR studies toward uncovering effective therapies for such diseases. Utilizing the known compound 6a as a starting template and guided by computational tools to derive physicochemical properties known to be important for CNS permeable drugs, the design and synthesis of a small series of novel triarylacrylonitrile analogues have been carried out providing compounds with enhanced potency and selectivity for PKC over the estrogen receptor relative to tamoxifen. Shortened synthetic routes compared to classical procedures have been developed for analogues incorporating a β-phenyl ring, which involve installing dialkylaminoalkoxy side chains first off the α and/or α' rings of a precursor benzophenone and then condensing the resultant ketones with phenylacetonitrile anion. A second novel, efficient and versatile route utilizing Suzuki chemistry has also been developed, which will allow for the introduction of a wide range of β-aryl or β-heteroaryl moieties and side-chain substituents onto the acrylonitrile core. For analogues possessing a single side chain off the α- or α'-ring, novel 2D NMR experiments have been carried out that allow for unambiguous assignment of E- and Z-stereochemistry. From the SAR analysis, one compound, 6c, shows markedly increased potency and selectivity for inhibiting PKC with an IC₅₀ of 80nM for inhibition of PKC protein substrate and >10μM for binding to the estrogen receptor α (tamoxifen IC₅₀=20μM and 222nM, respectively). The data on 6c provide support for further exploration of PKC as a druggable target for the treatment of amphetamine abuse.

Tamoxifen and amphetamine abuse: Are there therapeutic possibilities?

Although best known as a selective estrogen receptor modulator (SERM), tamoxifen is a drug with a wide range of activities. Tamoxifen has demonstrated some efficacy has a therapeutic for bipolar mania and is believed to exert these effects through inhibition of protein kinase C (PKC). As the symptoms of amphetamine treatment in rodents are believed to mimic the symptoms of a manic episode, many of the preclinical studies for this indication have demonstrated that tamoxifen inhibits amphetamine action. The amphetamine-induced increase in extracellular dopamine which gives rise to the 'manic' effects is due to interaction of amphetamine with the dopamine transporter. We and others have demonstrated that PKC reduces amphetamine-induced reverse transport through the dopamine transporter. In this review, we will outline the actions of tamoxifen as a SERM and further detail another known action of tamoxifen-inhibition of PKC. We will summarize the literature showing how tamoxifen affects amphetamine action. Finally, we will present our hypothesis that tamoxifen, or an analog, could be used therapeutically to reduce amphetamine abuse in addition to treating mania.

Molecular and Biochemical Analysis of the Estrogenic and Proliferative Properties of Vitamin E Compounds

Tocols are vitamin E compounds that include tocopherols (TPs) and tocotrienols (TTs). These lipophilic compounds are phenolic antioxidants and are reportedly able to modulate estrogen receptor β (ERβ). We investigated the molecular determinants that control their estrogenicity and effects on the proliferation of breast cancer cells. Docking experiments highlighted the importance of the tocol phenolic groups for their interaction with the ERs. Binding experiments confirmed that they directly interact with both ERα and ERβ with their isoforms showing potencies in the following order: δ-tocols > γ-tocols > α-tocols. We also found that tocols activated the transcription of an estrogen-responsive reporter gene that had been stably transfected into cells expressing either ERα or ERβ. The role of the phenolic group in tocol-ER interaction was further established using δ-tocopherylquinone, the oxidized form of δ-TP, which had no ER affinity and did not induce ER-dependent transcriptional modulation. Tocol activity also required the AF1 transactivation domain of ER. We found that both δ-TP and δ-TT stimulated the expression of endogenous ER-dependent genes. However, whereas δ-TP induced the proliferation of ER-positive breast cancer cells but not ER-negative breast cancer cells, δ-TT inhibited the proliferation of both ER-positive and ER-negative breast cancer cells. These effects of δ-TT were found to act through the down regulation of HMG-CoA reductase (HMGR) activity, establishing that ERs are not involved in this effect. Altogether, these data show that the reduced form of δ-TP has estrogenic properties which are lost when it is oxidized, highlighting the importance of the redox status in its estrogenicity. Moreover, we have shown that δ-TT has antiproliferative effects on breast cancer cells independently of their ER status through the inhibition of HMGR. These data clearly show that TPs can be discriminated from TTs according to their structure.

Steroid promiscuity: Diversity of enzyme action. Preface

This Special Issue on the topic of Steroid and Sterol Signaling: Promiscuity and Diversity, dwells on the growing realization that the 'one ligand, one binding site' and 'one enzyme, one reaction' concepts are out of date. Focusing on cytochromes P450 (CYP), hydroxysteroid dehydrogenases (HSDs), and related enzymes, the Special Issue highlights that a single enzyme can bind to diverse substrates, and in different conformations, and can catalyze multiple different conversions (and in different directions), thereby, generating an unexpectedly wide spectrum of ligands that can have subtly different biological actions. This article is part of a Special Issue entitled 'Steroid/Sterol Signaling' .

Tamoxifen regulation of sphingolipid metabolism--Therapeutic implications

Tamoxifen, a triphenylethylene antiestrogen and one of the first-line endocrine therapies used to treat estrogen receptor-positive breast cancer, has a number of interesting, off-target effects, and among these is the inhibition of sphingolipid metabolism. More specifically, tamoxifen inhibits ceramide glycosylation, and enzymatic step that can adventitiously support the influential tumor-suppressor properties of ceramide, the aliphatic backbone of sphingolipids. Additionally, tamoxifen and metabolites N-desmethyltamoxifen and 4-hydroxytamoxifen, have been shown to inhibit ceramide hydrolysis by the enzyme acid ceramidase. This particular intervention slows ceramide destruction and thereby depresses formation of sphingosine 1-phosphate, a mitogenic sphingolipid with cancer growth-promoting properties. As ceramide-centric therapies are becoming appealing clinical interventions in the treatment of cancer, agents like tamoxifen that can retard the generation of mitogenic sphingolipids and buffer ceramide clearance via inhibition of glycosylation, take on new importance. In this review, we present an abridged, lay introduction to sphingolipid metabolism, briefly chronicle tamoxifen's history in the clinic, examine studies that demonstrate the impact of triphenylethylenes on sphingolipid metabolism in cancer cells, and canvass works relevant to the use of tamoxifen as adjuvant to drive ceramide-centric therapies in cancer treatment. The objective is to inform the readership of what could be a novel, off-label indication of tamoxifen and structurally-related triphenylethylenes, an indication divorced from estrogen receptor status and one with application in drug resistance.

Modification of sphingolipid metabolism by tamoxifen and N-desmethyltamoxifen in acute myelogenous leukemia--Impact on enzyme activity and response to cytotoxics

The triphenylethylene antiestrogen, tamoxifen, can be an effective inhibitor of sphingolipid metabolism. This off-target activity makes tamoxifen an interesting ancillary for boosting the apoptosis-inducing properties of ceramide, a sphingolipid with valuable tumor censoring activity. Here we show for the first time that tamoxifen and metabolite, N-desmethyltamoxifen (DMT), block ceramide glycosylation and inhibit ceramide hydrolysis (by acid ceramidase, AC) in human acute myelogenous leukemia (AML) cell lines and in AML cells derived from patients. Tamoxifen (1-10 μM) inhibition of AC in AML cells was accompanied by decreases in AC protein expression. Tamoxifen also depressed expression and activity of sphingosine kinase 1 (SphK1), the enzyme-catalyzing production of mitogenic sphingosine 1-phosphate (S1-P). Results from mass spectroscopy showed that tamoxifen and DMT (i) increased the levels of endogenous C16:0 and C24:1 ceramide molecular species, (ii) nearly totally halted production of respective glucosylceramide (GC) molecular species, (iii) drastically reduced levels of sphingosine (to 9% of control), and (iv) reduced levels of S1-P by 85%, in vincristine-resistant HL-60/VCR cells. The co-administration of tamoxifen with either N-(4-hydroxyphenyl)retinamide (4-HPR), a ceramide-generating retinoid, or a cell-deliverable form of ceramide, C6-ceramide, resulted in marked decreases in HL-60/VCR cell viability that far exceeded single agent potency. Combination treatments resulted in synergistic apoptotic cell death as gauged by increased Annexin V binding and DNA fragmentation and activation of caspase-3. These results show the versatility of adjuvant triphenylethylene with ceramide-centric therapies for magnifying therapeutic potential in AML. Such drug regimens could serve as effective strategies, even in the multidrug-resistant setting.

Clinically used selective oestrogen receptor modulators increase LDL receptor activity in primary human lymphocytes

BACKGROUND AND PURPOSE

Treatment with selective oestrogen receptor modulators (SERMs) reduces low-density lipoprotein (LDL) cholesterol levels. We assessed the effect of tamoxifen, raloxifene and toremifene and their combinations with lovastatin on LDL receptor activity in lymphocytes from normolipidaemic and familial hypercholesterolaemic (FH) subjects, and human HepG2 hepatocytes and MOLT-4 lymphoblasts.

EXPERIMENTAL APPROACH

Lymphocytes were isolated from peripheral blood, treated with different compounds, and 1,1'-dioctadecyl-3,3,3,3'-tetramethylindocarbocyanine perchlorate (DiI)-labelled LDL uptake was analysed by flow cytometry.

KEY RESULTS

Tamoxifen, toremifene and raloxifene, in this order, stimulated DiI-LDL uptake by lymphocytes by inhibiting LDL-derived cholesterol trafficking and subsequent down-regulation of LDL receptor expression. Differently to what occurred in HepG2 and MOLT-4 cells, only tamoxifen consistently displayed a potentiating effect with lovastatin in primary lymphocytes. The SERM-mediated increase in LDL receptor activity was not altered by the anti-oestrogen ICI 182,780 nor was it reproduced by 17β-oestradiol. However, the tamoxifen-active metabolite endoxifen was equally effective as tamoxifen. The SERMs produced similar effects on LDL receptor activity in heterozygous FH lymphocytes as in normal lymphocytes, although none of them had a potentiating effect with lovastatin in heterozygous FH lymphocytes. The SERMs had no effect in homozygous FH lymphocytes.

CONCLUSIONS AND IMPLICATIONS

Clinically used SERMs up-regulate LDL receptors in primary human lymphocytes. There is a mild enhancement between SERMs and lovastatin of lymphocyte LDLR activity, the potentiation being greater in HepG2 and MOLT-4 cells. The effect of SERMs is independent of oestrogen receptors but is preserved in the tamoxifen-active metabolite endoxifen. This mechanism may contribute to the cholesterol-lowering action of SERMs.

Steroid signaling: ligand-binding promiscuity, molecular symmetry, and the need for gating

Steroid/sterol-binding receptors and enzymes are remarkably promiscuous in the range of ligands they can bind to and, in the case of enzymes, modify - raising the question of how specific receptor activation is achieved in vivo. Estrogen receptors (ER) are modulated by 27-hydroxycholesterol and 5α-androstane-3β,17β-diol (Adiol), in addition to estradiol (E2), and respond to diverse small molecules such as bisphenol A. Steroid-modifying enzymes are also highly promiscuous in ligand binding and metabolism. The specificity problem is compounded by the fact that the steroid core (hydrogenated cyclopentophenanthrene ring system) has several planes of symmetry. Ligand binding can be in symmetrical East-West (rotation) and North-South (inversion) orientations. Hydroxysteroid dehydrogenases (HSDs) can modify symmetrical 7 and 11, also 3 and 17/20, positions, exemplified here by yeast 3α,20β-HSD and mammalian 11β-HSD and 17β-HSD enzymes. Faced with promiscuity and symmetry, other strategies are clearly necessary to promote signaling selectivity in vivo. Gating regulates hormone access via enzymes that preferentially inactivate (or activate) a subclass of ligands, thereby governing which ligands gain receptor access - exemplified by 11β-HSD gating cortisol access to the mineralocorticoid receptor, and P450 CYP7B1 gating Adiol access to ER. Counter-intuitively, the specificity of steroid/sterol action is achieved not by intrinsic binding selectivity but by the combination of local metabolism and binding affinity.

Effects of adjuvant aromatase inhibitor therapy on lipid profiles

How aromatase inhibitors affect lipids is of great interest. Compared with tamoxifen, adjuvant anastrozole and letrozole are associated with increased incidences of hypercholesterolemia, while similar data are lacking for exemestane in the adjuvant setting. No significant differences in lipid profiles occurred with extended adjuvant exemestane compared with placebo, but total cholesterol and low-density lipoprotein levels increased significantly above baseline in both groups over 6 months. Likewise, no significant differences in hypercholesterolemia rates occurred between extended adjuvant letrozole and placebo. A lipid substudy further confirmed that letrozole did not significantly alter serum lipids for 36 months compared with placebo. Thus, although aromatase inhibitors lack the lipid-lowering properties of tamoxifen, no significant worsening of lipid levels occurs with their use. Patients would benefit from lifestyle changes and routine monitoring of serum lipids. Breast cancer therapy trials often report serum lipid parameters, but assessing the quality and overall significance of the data can be difficult. Methodology of data collection varies among trials and the concomitant use of lipid-modifying medication is often not reported. This review discusses the current understanding of the influence of lipid levels on cardiovascular risk in women and presents key findings on the effects of adjuvant aromatase inhibitor therapy on lipid profiles.

Vitamin C suppresses cell death in MCF-7 human breast cancer cells induced by tamoxifen

Vitamin C is generally thought to enhance immunity and is widely taken as a supplement especially during cancer treatment. Tamoxifen (TAM) has both cytostatic and cytotoxic properties for breast cancer. TAM engaged mitochondrial oestrogen receptor beta in MCF-7 cells and induces apoptosis by activation of pro-caspase-8 followed by downstream events, including an increase in reactive oxygen species and the release of pro-apoptotic factors from the mitochondria. In addition to that, TAM binds with high affinity to the microsomal anti-oestrogen-binding site and inhibits cholesterol esterification at therapeutic doses. This study aimed to investigate the role of vitamin C in TAM-mediated apoptosis. Cells were loaded with vitamin C by exposure to dehydroascorbic acid, thereby circumventing in vitro artefacts associated with the poor transport and pro-oxidant effects of ascorbic acid. Pre-treatment with vitamin C caused a dose-dependent attenuation of cytotoxicity, as measured by acridine-orange/propidium iodide (AO/PI) and Annexin V assay after treatment with TAM. Vitamin C dose-dependently protected cancer cells against lipid peroxidation caused by TAM treatment. By real-time PCR analysis, an impressive increase in FasL and tumour necrosis factor-α (TNF-α) mRNA was detected after TAM treatment. In addition, a decrease in mitochondrial transmembrane potential was observed. These results support the hypothesis that vitamin C supplementation during cancer treatment may detrimentally affect therapeutic response.

S6K1 inhibition enhances tamoxifen-induced cell death in MCF-7 cells through translational inhibition of Mcl-1 and survivin

S6 kinase 1 (S6K1) was suggested to be a marker for endocrine therapy resistance in breast cancer. We examined whether tamoxifen's effect can be modulated by S6K1 inhibition. S6K1 inhibition by PF4708671, a selective inhibitor of S6K1, acts synergistically with tamoxifen in S6K1-high MCF-7 cells. Similarly, the knockdown of S6K1 with small interfering RNA (siRNA) significantly sensitized MCF-7 cells to tamoxifen. Inhibition of S6K1 by PF4708671 led to a marked decrease in the expression levels of the anti-apoptotic proteins Mcl-1 and survivin, which was not related to mRNA levels. In addition, suppression of Mcl-1 or survivin, using specific siRNA, further enhanced cell sensitivity to tamoxifen. These results showed that inhibition of S6K1 acts synergistically with tamoxifen, via translational modulation of Mcl-1 and survivin. Based on these findings, we propose that targeting S6K1 may be an effective strategy to overcome tamoxifen resistance in breast cancer.

Novel off-target effect of tamoxifen--inhibition of acid ceramidase activity in cancer cells

Acid ceramidase (AC), EC 3.5.1.23, a lysosomal enzyme, catalyzes the hydrolysis of ceramide to constituent sphingoid base, sphingosine, and fatty acid. Because AC regulates the levels of pro-apoptotic ceramide and mitogenic sphingosine-1-phosphate, it is considered an apt target in cancer therapy. The present study reveals, for the first time, that the prominent antiestrogen, tamoxifen, is a pan-effective AC inhibitor in the low, single digit micromolar range, as demonstrated in a wide spectrum of cancer cell types, prostate, pancreatic, colorectal, and breast. Prostate cancer cells were chosen for the detailed investigations. Treatment of intact PC-3 cells with tamoxifen produced time- and dose-dependent inhibition of AC activity. Tamoxifen did not impact cell viability nor did it inhibit AC activity in cell-free assays. In pursuit of mechanism of action, we demonstrate that tamoxifen induced time-, as early as 5min, and dose-dependent, as low as 5μM, increases in lysosomal membrane permeability (LMP), and time- and dose-dependent downregulation of AC protein expression. Assessing various protease inhibitors revealed that a cathepsin B inhibitor blocked tamoxifen-elicited downregulation of AC protein; however, this action failed to restore AC activity unless assayed in a cell-free system at pH4.5. In addition, pretreatment with tamoxifen inhibited PC-3 cell migration. Toremifene, an antiestrogen structurally similar to tamoxifen, was also a potent inhibitor of AC activity. This study reveals a new, off-target action of tamoxifen that may be of benefit to enhance anticancer therapies that either incorporate ceramide or target ceramide metabolism.

5,6-Epoxy-cholesterols contribute to the anticancer pharmacology of tamoxifen in breast cancer cells

Tamoxifen (Tam) is a selective estrogen receptor modulator (SERM) that remains one of the major drugs used in the hormonotherapy of breast cancer (BC). In addition to its SERM activity, we recently showed that the oxidative metabolism of cholesterol plays a role in its anticancer pharmacology. We established that these effects were not regulated by the ER but by the microsomal antiestrogen binding site/cholesterol-5,6-epoxide hydrolase complex (AEBS/ChEH). The present study aimed to identify the oxysterols that are produced under Tam treatment and to define their mechanisms of action. Tam and PBPE (a selective AEBS/ChEH ligand) stimulated the production and the accumulation of 5,6α-epoxy-cholesterol (5,6α-EC), 5,6α-epoxy-cholesterol-3β-sulfate (5,6-ECS), 5,6β-epoxy-cholesterol (5,6β-EC) in MCF-7 cells through a ROS-dependent mechanism, by inhibiting ChEH and inducing sulfation of 5,6α-EC by SULT2B1b. We showed that only 5,6α-EC was responsible for the induction of triacylglycerol (TAG) biosynthesis by Tam and PBPE, through the modulation of the oxysterol receptor LXRβ. The cytotoxicity mediated by Tam and PBPE was triggered by 5,6β-EC through an LXRβ-independent route and by 5,6-ECS through an LXRβ-dependent mechanism. The importance of SULT2B1b was confirmed by its ectopic expression in the SULT2B1b(-) MDA-MB-231 cells, which became sensitive to 5,6α-EC, Tam or PBPE at a comparable level to MCF-7 cells. This study established that 5,6-EC metabolites contribute to the anticancer pharmacology of Tam and highlights a novel signaling pathway that points to a rationale for re-sensitizing BC cells to Tam and AEBS/ChEH ligands.

4-hydroxytamoxifen leads to PrPSc clearance by conveying both PrPC and PrPSc to lysosomes independently of autophagy

Prion diseases are fatal neurodegenerative disorders involving the abnormal folding of a native cellular protein, named PrP(C), to a malconformed aggregation-prone state, enriched in beta sheet secondary structure, denoted PrP(Sc). Recently, autophagy has garnered considerable attention as a cellular process with the potential to counteract neurodegenerative diseases of protein aggregation such as Alzheimer's disease, Huntington's disease, and Parkinson's disease. Stimulation of autophagy by chemical compounds has also been shown to reduce PrP(Sc) in infected neuronal cells and prolong survival times in mouse models. Consistent with previous reports, we demonstrate that autophagic flux is increased in chronically infected cells. However, in contrast to recent findings we show that autophagy does not cause a reduction in scrapie burden. We report that in infected neuronal cells different compounds known to stimulate autophagy are ineffective in increasing autophagic flux and in reducing PrP(Sc). We further demonstrate that tamoxifen and its metabolite 4-hydroxytamoxifen lead to prion degradation in an autophagy-independent manner by diverting the trafficking of both PrP and cholesterol to lysosomes. Our data indicate that tamoxifen, a well-characterized, widely available pharmaceutical, may have applications in the therapy of prion diseases.

Cholesterol and the development of clear-cell renal carcinoma

The majority of kidney cancers are clear-cell carcinomas (ccRCC), characterized by the accumulation of cholesterol, cholesterol esters, other neutral lipids and glycogen. Rather than being a passive bystander, the clear-cell phenotype is suggested to be a biomarker of deregulated cholesterol and lipid biosynthesis, which plays an important role in development of the disease. One clue to this relationship has come from the elucidation of the hereditary kidney cancer gene, TRC8, which functions partly to degrade key regulators of endogenous cholesterol and lipid biosynthesis. In addition, deregulation of the mevalonate pathway has been shown to play a key role in cellular transformation and invasion. These findings are supported by considerable epidemiologic data linking obesity and the deregulation of lipid biosynthesis to ccRCC.

Anti-thrombotic effects of selective estrogen receptor modulator tamoxifen

Tamoxifen is a known anti-cancer drug and established estrogen receptor modulator. Few clinical studies have earlier implicated the drug in thrombotic complications attributable to lower anti-thrombin and protein S levels in plasma. However, action of tamoxifen on platelet signalling machinery has not been elucidated in detail. In the present report we show that tamoxifen is endowed with significant inhibitory property against human platelet aggregation. From a series of in vivo and in vitro studies tamoxifen was found to inhibit almost all platelet functions, prolong tail bleeding time in mouse and profoundly prevent thrombus formation at injured arterial wall in mice, as well as on collagen matrix perfused with platelet-rich plasma under arterial shear against the vehicle dimethylsulfoxide (DMSO). These findings strongly suggest that tamoxifen significantly downregulates platelet responses and holds potential as a promising anti-platelet/anti-thrombotic agent.

Auraptene is an inhibitor of cholesterol esterification and a modulator of estrogen receptors

Auraptene is a prenyloxycoumarin from Citrus species with chemopreventive properties against colitis-related colon and breast cancers through a yet-undefined mechanism. To decipher its mechanism of action, we used a ligand-structure based approach. We established that auraptene fits with a pharmacophore involved in both the inhibition of acyl-CoA:cholesterol acyl transferase (ACAT) and the modulation of estrogen receptors (ERs). We confirmed experimentally that auraptene inhibits ACAT and binds to ERs in a concentration-dependent manner and that it inhibited ACAT in rat liver microsomes and in intact cancer cells of murine and human origins, with an IC(50) value in the micromolar range. Auraptene bound to ERs with affinities of 7.8 μM for ERα and 7.9 μM for ERβ, stabilized ERs, and modulated their transcriptional activity via an ER-dependent reporter gene and endogenous genes. We further established that these effects correlated well with the control of growth and invasiveness of tumor cells. Our data shed light on the molecular mechanism underlying the anticancer and chemopreventive effects of auraptene.

Chylomicron- and VLDL-derived lipids enter the heart through different pathways: in vivo evidence for receptor- and non-receptor-mediated fatty acid uptake

Lipids circulate in the blood in association with plasma lipoproteins and enter the tissues either after hydrolysis or as non-hydrolyzable lipid esters. We studied cardiac lipids, lipoprotein lipid uptake, and gene expression in heart-specific lipoprotein lipase (LpL) knock-out (hLpL0), CD36 knock-out (Cd36(-/-)), and double knock-out (hLpL0/Cd36(-/-)-DKO) mice. Loss of either LpL or CD36 led to a significant reduction in heart total fatty acyl-CoA (control, 99.5 ± 3.8; hLpL0, 36.2 ± 3.5; Cd36(-/-), 57.7 ± 5.5 nmol/g, p < 0.05) and an additive effect was observed in the DKO (20.2 ± 1.4 nmol/g, p < 0.05). Myocardial VLDL-triglyceride (TG) uptake was reduced in the hLpL0 (31 ± 6%) and Cd36(-/-) (47 ± 4%) mice with an additive reduction in the DKO (64 ± 5%) compared with control. However, LpL but not CD36 deficiency decreased VLDL-cholesteryl ester uptake. Endogenously labeled mouse chylomicrons were produced by tamoxifen treatment of β-actin-MerCreMer/LpL(flox/flox) mice. Induced loss of LpL increased TG levels >10-fold and reduced HDL by >50%. After injection of these labeled chylomicrons in the different mice, chylomicron TG uptake was reduced by ∼70% and retinyl ester by ∼50% in hLpL0 hearts. Loss of CD36 did not alter either chylomicron TG or retinyl ester uptake. LpL loss did not affect uptake of remnant lipoproteins from ApoE knock-out mice. Our data are consistent with two pathways for fatty acid uptake; a CD36 process for VLDL-derived fatty acid and a non-CD36 process for chylomicron-derived fatty acid uptake. In addition, our data show that lipolysis is involved in uptake of core lipids from TG-rich lipoproteins.

Rimonabant is a dual inhibitor of acyl CoA:cholesterol acyltransferases 1 and 2

Acyl coenzyme A:cholesterol acyltransferase (ACAT) catalyzes the intracellular synthesis of cholesteryl esters (CE). Both ACAT isoforms, ACAT1 and ACAT2, play key roles in the pathophysiology of atherosclerosis and ACAT inhibition retards atherosclerosis in animal models. Rimonabant, a type 1 cannabinoid receptor (CB1) antagonist, produces anti-atherosclerotic effects in humans and animals by mechanisms which are not completely understood. Rimonabant is structurally similar to two other cannabinoid receptor antagonists, AM251 and SR144528, recently identified as potent inhibitors of ACAT. Therefore, we examined the effects of Rimonabant on ACAT using both in vivo cell-based assays and in vitro cell-free assays. Rimonabant dose-dependently reduced ACAT activity in Raw 264.7 macrophages (IC(50)=2.9+/-0.38 microM) and isolated peritoneal macrophages. Rimonabant inhibited ACAT activity in intact CHO-ACAT1 and CHO-ACAT2 cells and in cell-free assays with approximately equal efficiency (IC(50)=1.5+/-1.2 microM and 2.2+/-1.1 microM for CHO-ACAT1 and CHO-ACAT2, respectively). Consistent with ACAT inhibition, Rimonabant treatment blocked ACAT-dependent processes in macrophages, oxysterol-induced apoptosis and acetylated-LDL induced foam cell formation. From these results we conclude that Rimonabant is an ACAT1/2 dual inhibitor and suggest that some of the atherosclerotic beneficial effects of Rimonabant are, at least partly, due to inhibition of ACAT.

Identification and pharmacological characterization of cholesterol-5,6-epoxide hydrolase as a target for tamoxifen and AEBS ligands

The microsomal antiestrogen binding site (AEBS) is a high-affinity target for the antitumor drug tamoxifen and its cognate ligands that mediate breast cancer cell differentiation and apoptosis. The AEBS, a hetero-oligomeric complex composed of 3beta-hydroxysterol-Delta8-Delta7-isomerase (D8D7I) and 3beta-hydroxysterol-Delta7-reductase (DHCR7), binds different structural classes of ligands, including ring B oxysterols. These oxysterols are inhibitors of cholesterol-5,6-epoxide hydrolase (ChEH), a microsomal epoxide hydrolase that has yet to be molecularly identified. We hypothesized that the AEBS and ChEH might be related entities. We show that the substrates of ChEH, cholestan-5alpha,6alpha-epoxy-3beta-ol (alpha-CE) and cholestan-5beta,6beta-epoxy-3beta-ol (beta-CE), and its product, cholestane-3beta,5alpha,6beta-triol (CT), are competitive ligands of tamoxifen binding to the AEBS. Conversely, we show that each AEBS ligand is an inhibitor of ChEH activity, and that there is a positive correlation between these ligands' affinity for the AEBS and their potency to inhibit ChEH (r2=0.95; n=39; P<0.0001). The single expression of D8D7I or DHCR7 in COS-7 cells slightly increased ChEH activity (1.8- and 2.6-fold), whereas their coexpression fully reconstituted ChEH, suggesting that the formation of a dimer is required for ChEH activity. Similarly, the single knockdown of D8D7I or DHCR7 using siRNA partially inhibited ChEH in MCF-7 cells, whereas the knockdown of both D8D7I and DHCR7 abolished ChEH activity by 92%. Taken together, our findings strongly suggest that the AEBS carries out ChEH activity and establish that ChEH is a new target for drugs of clinical interest, polyunsaturated fatty acids and ring B oxysterols.

Estrogen decreases atherosclerosis in part by reducing hepatic acyl-CoA:cholesterol acyltransferase 2 (ACAT2) in monkeys

OBJECTIVE

Estrogens decrease atherosclerosis progression, mediated in part through changes in plasma lipids and lipoproteins. This study aimed to determine estrogen-induced changes in hepatic cholesterol metabolism, plasma lipoproteins, and the relationship of these changes to atherosclerosis extent.

METHODS AND RESULTS

Ovariectomized monkeys (n=34) consumed atherogenic diets for 30 months which contained either no hormones (control, n=17) or conjugated equine estrogens (CEE, n=17) at a human dose equivalent of 0.625 mg/d. Hepatic cholesterol content, low-density lipoprotein (LDL) receptor expression, cholesterol 7 alpha-hydroxylase and acyl-coenzyme A:cholesterol acyltransferase (ACAT) activity, and expression levels were determined. CEE treatment resulted in lower plasma concentrations of very-low- and intermediate- density lipoprotein cholesterol (V+IDLC; P=0.01), smaller LDL particles (P=0.002), and 50% lower hepatic cholesterol content (total, free, and esterified; P<0.05 for all). Total ACAT activity was significantly lower (P=0.01), explained primarily by reductions in the activity of ACAT2. Estrogen regulation of enzymatic activity was at the protein level as both ACAT1 and 2 protein, but not mRNA levels, were lower (P=0.02 and <0.0001, respectively). ACAT2 activity was significantly associated with hepatic total cholesterol, plasma V+IDLC cholesterol, and atherosclerosis.

CONCLUSIONS

Atheroprotective effects of estrogen therapy may be related to reduced hepatic secretion of ACAT2-derived cholesteryl esters in plasma lipoproteins.

Assessment of vascular effects of tamoxifen and its metabolites on the rat perfused hindquarter vascular bed

Tamoxifen has been suggested to produce beneficial cardiovascular effects, although the mechanisms for these effects are not fully known. Moreover, although tamoxifen metabolites may exhibit 30-100 times higher potency than the parent drug, no previous study has compared the effects produced by tamoxifen and its metabolites on vascular function. Here, we assessed the vascular responses to acetylcholine and sodium nitroprusside on perfused hindquarter vascular bed of rats treated with tamoxifen or its main metabolites (N-desmethyl-tamoxifen, 4-hydroxy-tamoxifen, and endoxifen) for 2 weeks. Plasma and whole-blood thiobarbituric acid reactive substances (TBARS) concentrations were determined using a fluorometric method. Plasma nitrite and NOx (nitrite + nitrate) concentrations were determined using an ozone-based chemiluminescence assay and Griess reaction, respectively. Treatment with tamoxifen reduced the responses to acetylcholine (pD(2) = 2.2 +/- 0.06 and 1.9 +/- 0.05 after vehicle and tamoxifen, respectively; P < 0.05), while its metabolites improved these responses (pD(2) = 2.5 +/- 0.04 after N-desmethyl-tamoxifen, 2.5 +/- 0.03 after 4-hydroxy-tamoxifen, and 2.6 +/- 0.08 after endoxifen; P < 0.01). Tamoxifen and its metabolites showed no effect on endothelial-independent responses to sodium nitroprusside (P > 0.05). While tamoxifen treatment resulted in significantly higher plasma and whole blood lipid peroxide levels (37% and 62%, respectively; both P < 0.05), its metabolites significantly decreased lipid peroxide levels (by approximately 50%; P < 0.05). While treatment with tamoxifen decreased the concentrations of markers of nitric oxide formation by approximately 50% (P < 0.05), tamoxifen metabolites had no effect on these parameters (P > 0.05). These results suggest that while tamoxifen produces detrimental effects, its metabolites produce counteracting beneficial effects on the vascular system and on nitric oxide/reactive oxygen species formation.

Signaling through cholesterol esterification: a new pathway for the cholecystokinin 2 receptor involved in cell growth and invasion

Several studies indicate that cholesterol esterification is deregulated in cancers. The present study aimed to characterize the role of cholesterol esterification in proliferation and invasion of two tumor cells expressing an activated cholecystokinin 2 receptor (CCK2R). A significant increase in cholesterol esterification and activity of Acyl-CoA:cholesterol acyltransferase (ACAT) was measured in tumor cells expressing a constitutively activated oncogenic mutant of the CCK2R (CCK2R-E151A cells) compared with nontumor cells expressing the wild-type CCK2R (CCK2R-WT cells). Inhibition of cholesteryl ester formation and ACAT activity by Sah58-035, an inhibitor of ACAT, decreased by 34% and 73% CCK2R-E151A cell growth and invasion. Sustained activation of CCK2R-WT cells by gastrin increased cholesteryl ester production while addition of cholesteryl oleate to the culture medium of CCK2R-WT cells increased cell proliferation and invasion to a level close to that of CCK2R-E151A cells. In U87 glioma cells, a model of autocrine growth stimulation of the CCK2R, inhibition of cholesterol esterification and ACAT activity by Sah58-035 and two selective antagonists of the CCK2R significantly reduced cell proliferation and invasion. In both models, cholesteryl ester formation was found dependent on protein kinase zeta/ extracellular signal-related kinase 1/2 (PKCzeta/ERK1/2) activation. These results show that signaling through ACAT/cholesterol esterification is a novel pathway for the CCK2R that contributes to tumor cell proliferation and invasion.

AM-251 and SR144528 are acyl CoA:cholesterol acyltransferase inhibitors

Oxysterol-induced macrophage apoptosis may have a role in atherosclerosis. Macrophages lacking the type 2 cannabinoid receptor (CB2) are partially resistant to apoptosis induced by 7-ketocholesterol (7KC). AM-251 and SR144528 are selective antagonists of CB1 and CB2 receptors, respectively. We observed that both compounds reduce 7KC-induced apoptosis in Raw 264.7 macrophages. As oxysterol-induced macrophage apoptosis requires acyl-coenzymeA:cholesterol acyltransferase (ACAT) activity, we tested their affects on ACAT activity. AM-251 and SR144528 both reduced cholesteryl ester synthesis in unstimulated and acetylated LDL-stimulated Raw 264.7 macrophages, CB2(+/+) and CB2(-/-) peritoneal macrophages, as well as in vitro, in mouse liver microsomes. Consistent with inhibition of ACAT, the development of foam cell characteristics in macrophages by treatment with acetylated LDL was reduced by both compounds. This work is the first evidence that AM-251 and SR144528 are inhibitors of ACAT and as a result, might have anti-atherosclerotic activities independent of their affect on cannabinoid signaling.

Microsomal antiestrogen-binding site ligands induce growth control and differentiation of human breast cancer cells through the modulation of cholesterol metabolism

The microsomal antiestrogen-binding site (AEBS) is a high-affinity membranous binding site for the antitumor drug tamoxifen that selectively binds diphenylmethane derivatives of tamoxifen such as PBPE and mediates their antiproliferative properties. The AEBS is a hetero-oligomeric complex consisting of 3beta-hydroxysterol-Delta8-Delta7-isomerase and 3beta-hydroxysterol-Delta7-reductase. High-affinity AEBS ligands inhibit these enzymes leading to the massive intracellular accumulation of zymostenol or 7-dehydrocholesterol (DHC), thus linking AEBS binding to the modulation of cholesterol metabolism and growth control. The aim of the present study was to gain more insight into the control of breast cancer cell growth by AEBS ligands. We report that PBPE and tamoxifen treatment induced differentiation in human breast adenocarcinoma cells MCF-7 as indicated by the arrest of cells in the G0-G1 phase of the cell cycle, the increase in the cell volume, the accumulation and secretion of lipids, and a milk fat globule protein found in milk. These effects were observed with other AEBS ligands and with zymostenol and DHC. Vitamin E abrogates the induction of differentiation and reverses the control of cell growth produced by AEBS ligands, zymostenol, and DHC, showing the importance of the oxidative processes in this effect. AEBS ligands induced differentiation in estrogen receptor-negative mammary tumor cell lines SKBr-3 and MDA-MB-468 but with a lower efficiency than observed with MCF-7. Together, these data show that AEBS ligands exert an antiproliferative effect on mammary cancer cells by inducing cell differentiation and growth arrest and highlight the importance of cholesterol metabolism in these effects.

Guar gum consumption increases hepatic nuclear SREBP2 and LDL receptor expression in pigs fed an atherogenic diet

To gain insight into the regulation of hepatic sterol-responsive genes that are thought to mediate the hypocholesterolemic effects of guar gum (GG) consumption, the mRNA and protein expression of sterol regulatory element binding protein 2 (SREBP2), LDL receptor (LDLr), and scavenger receptor class B, type 1 (SR-B1) were examined in pigs consuming an atherogenic control diet or the control diet supplemented with 10% GG. Compared with the control group, GG consumption reduced (P < 0.05) plasma total cholesterol and LDL cholesterol concentrations by 27 and 37%, respectively. Furthermore, hepatic free cholesterol concentration was lower (P < 0.05) in the GG-fed pigs in comparison with the control group. GG consumption increased hepatic LDLr mRNA (1.5-fold of the control, P = 0.09) and protein (2-fold of the control, P < 0.05) expression in comparison with the control group. However, GG consumption reduced hepatic SR-B1 mRNA to 36% of the control (P < 0.05) expression but did not affect (P = 0.19) SR-B1 protein abundance in comparison with the control group. Although SREBP2 mRNA expression was similar (P = 0.89) in the 2 groups, GG consumption increased (P < 0.05) the expression of the cytoplasmic precursor (3-fold of the control) and nuclear active forms (1.5-fold of the control) of SREBP2. We conclude that the hypocholesterolemic effects of GG consumption are related to a reduction in hepatic free cholesterol concentration and associated increases in nuclear active SREBP2 expression and hepatic LDLr abundance.

Influence of gender on tamoxifen-induced biochemical changes in serum of rats

Tamoxifen, the widely prescribed drug in the prevention and therapy of breast cancer, may cause side effects which may be influenced by gender. The present study was undertaken to investigate the impact of gender on tamoxifen-induced toxic and biochemical changes following oral administration of tamoxifen at high dose level of 20 mg/kg once daily for a 2-week period in both male and female rats. The results showed marked increases in serum activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in female rats. In contrast, treatment with tamoxifen in male animals significantly decreased the activity of ALT, with a tendency for a decrease in serum AST levels. In female rats, a significant reduction in the serum activity of acid phosphatase (ACP) was noted, compared with a non-significant decrease in males. Non-significant changes in serum levels of alkaline phosphatase (ALP) were seen in both sexes. Tamoxifen lowered serum contents of total lipid and total cholesterol in both male and female rats. Serum levels of triglycerides were reduced in female rats as compared to a non-significant decrease in male animals. The serum albumin concentration was decreased in both male and female rats, while total protein was decreased only in female animals. Tamoxifen markedly increased serum levels of creatinine in female rats, compared with a non-significant rise in males. Total serum contents of calcium were similarly reduced in both males and females. This is the first study which points to gender-related differences in tamoxifen-induced toxic and metabolic changes in rats. The results indicated that females are more susceptible than males to tamoxifen toxicity, probably due to the ability of tamoxifen to antagonize the action of estrogen in females.

The prototypical inhibitor of cholesterol esterification, Sah 58-035 [3-[decyldimethylsilyl]-n-[2-(4-methylphenyl)-1-phenylethyl]propanamide], is an agonist of estrogen receptors

We have shown recently that estrogen receptor (ER) ligands share a diphenyl ethane pharmacophore with Sah 58-035 [3-[decyldimethylsilyl]-N-[2-(4-methylphenyl)-1-phenylethyl]-propanamide], a prototypical inhibitor of the acyl-cholesterolacyl-transferase (ACAT), which enabled us to establish that ER ligands were potent inhibitors of ACAT and blocked the formation of foam cells. In the present study, we have tested whether this structural similarity means that Sah 58-035 is an ER modulator. We report that Sah 58-035 bound to ERalpha and ERbeta with an IC(50) of 2.9 and 3.1 microM, respectively. Docking studies using molecular modeling of Sah 58-035 with the X-ray structure of the ER showed that Sah 58-035 fits well into the ligand binding site known for 4-hydroxy-tamoxifen. Despite having high three-dimensional structural similarities with the pure antiestrogen ICI 164,384 [(N-n-butyl-N-methyl-11-[3,17beta-di-hydroxyestra-1,3, 5(10)-trien-7alpha-yl]-undecanamide], we showed that Sah 58-035 is an agonist of ER for transcription and cellular proliferation. These data showed that Sah 58-035 was an estrogen receptor agonist and that the size and the chemical nature of the side chain were critical for agonist versus antagonist activity on ER. This new molecular mechanism of action for Sah 58-035 has to be taken into account in understanding better its pharmacological activities. Moreover, these data give new structural insights into the understanding of agonist versus antagonist activities of ER ligands and also for the conception of new drugs with a dual ACAT inhibition and ER modulation potential and their evaluation in different pathologies where both targets are involved, such as atherosclerosis, Alzheimer's disease, and cancer.