Five decades with oxysterols

The Hylemon-Björkhem pathway of bile acid 7-dehydroxylation: history, biochemistry, and microbiology

Bile acids are detergents derived from cholesterol that function to solubilize dietary lipids, remove cholesterol from the body, and act as nutrient signaling molecules in numerous tissues with functions in the liver and gut being the best understood. Studies in the early 20th century established the structures of bile acids, and by mid-century, the application of gnotobiology to bile acids allowed differentiation of host-derived "primary" bile acids from "secondary" bile acids generated by host-associated microbiota. In 1960, radiolabeling studies in rodent models led to determination of the stereochemistry of the bile acid 7-dehydration reaction. A two-step mechanism was proposed, which we have termed the Samuelsson-Bergström model, to explain the formation of deoxycholic acid. Subsequent studies with humans, rodents, and cell extracts of Clostridium scindens VPI 12708 led to the realization that bile acid 7-dehydroxylation is a result of a multi-step, bifurcating pathway that we have named the Hylemon-Björkhem pathway. Due to the importance of hydrophobic secondary bile acids and the increasing measurement of microbial bai genes encoding the enzymes that produce them in stool metagenome studies, it is important to understand their origin.

Role of white matter hyperintensity in effects of apolipoprotein E on cognitive injury

Magnetic Resonance Imaging (MRI) T2-weighted white matter hyperintensity (WMH) is a marker of small vessel cerebrovascular pathology and is of ischemic origin. The prevalence and severity of WMH is associated with cardiovascular risk factors, aging, and cognitive injury in mild cognitive impairment (MCI), vascular dementia, and Alzheimer's disease (AD). WMH especially affects executive function, with additional effects on memory and global cognition. Apolipoprotein E (apoE) plays a role in cholesterol metabolism and neuronal repair after injury. Human and animal studies support a role for apoE in maintaining white matter integrity. In humans, there are three major human apoE isoforms, E2, E3, and E4. Human apoE isoforms differ in risk to develop AD and in association with WMH. In this Mini Review, we propose an increased focus on the role of WMH in cognitive health and cognitive injury and the likely role of apoE and apoE isoform in modulating these effects. We hypothesize that apoE and apoE isoforms play a role in modulating WMH via apoE isoform-dependent effects on oxylipins and 7-ketocholesterol, as well as amyloid related vascular injury, as seen in cerebral amyloid angiopathy.

Oxysterols in catfish skin secretions (Arius bilineatus, Val.) exhibit anti-cancer properties

The edible catfish Arius bilineatus, (Valenciennes) elaborates a proteinaceous gel-like material through its epidermis when threatened or injured. Our on-going studies on this gel have shown it to be a complex mixture of several biologically active molecules. Anti-cancer studies on lipid fractions isolated from the gel-like materials showed them to be active against several cancer cell lines. This prompted us to investigate further the lipid composition of the catfish epidermal gel secretions (EGS). Analysis of the lipid fraction of EGS resulted in identification of 12 oxysterols including cholesterol and 2 deoxygenated steroids i.e., 7α-hydroxy cholesterol, 7β-hydroxycholesterol, 5,6 epoxycholesterol, 3β-hydroxycholest-5-ene-7-one and cholesta-3,5-dien-7-one. Progesterone, cholest-3,5-diene, cholesta-2,4-diene, cholest-3,5,6-triol and 4-cholesten-3-one were found as minor components, and were identified through their MS, ¹HNMR and FTIR spectral data and were compared with those of the standards. Cholest-3,6-dione, cholesta-4,6-diene-3-one, cholesta-2,4-diene, and cholesta-5,20(22)-dien-3-ol were found only in trace amounts and were identified by GC/MS/MS spectral data. Since cholesterol is the major component of EGS, the identified oxysterols (OS) are presumably cholesterol oxidation products. Many of the identified OS are known important biological molecules that play vital physiological role in the producer and recipient organisms. We report herein the effects of these sterols on three human cancer cell lines in vitro, i.e., K-562 (CML cell line), MDA MB-231 (estrogen positive breast cancer cell line) and MCF-7 (estrogen negative breast cancer cell line). Interestingly significant (p < 0.05) dose differences were observed between tested OS on cell types used. The presence of these sterols in EGS may help explain some aspects of the physiological activities of fraction B (FB) prepared from EGS, such as enhanced wound and diabetic ulcer healing, anti-inflammatory action and cytotoxic activities reported in our previous studies. The anti-proliferative actions of some of these oxysterols especially the cholesterol 3,5,6-triol (#5) as established on selected cancer cell lines in this study support our previous studies and make them candidates for research for human application.

Oxysterols are potential physiological regulators of ageing

Delaying and even reversing ageing is a major public health challenge with a tremendous potential to postpone a plethora of diseases including cancer, metabolic syndromes and neurodegenerative disorders. A better understanding of ageing as well as the development of innovative anti-ageing strategies are therefore an increasingly important field of research. Several biological processes including inflammation, proteostasis, epigenetic, oxidative stress, stem cell exhaustion, senescence and stress adaptive response have been reported for their key role in ageing. In this review, we describe the relationships that have been established between cholesterol homeostasis, in particular at the level of oxysterols, and ageing. Initially considered as harmful pro-inflammatory and cytotoxic metabolites, oxysterols are currently emerging as an expanding family of fine regulators of various biological processes involved in ageing. Indeed, depending of their chemical structure and their concentration, oxysterols exhibit deleterious or beneficial effects on inflammation, oxidative stress and cell survival. In addition, stem cell differentiation, epigenetics, cellular senescence and proteostasis are also modulated by oxysterols. Altogether, these data support the fact that ageing is influenced by an oxysterol profile. Further studies are thus required to explore more deeply the impact of the "oxysterome" on ageing and therefore this cholesterol metabolic pathway constitutes a promising target for future anti-ageing interventions.

Apolipoprotein E Isoform-specific changes related to stress and trauma exposure

Post-Traumatic Stress Disorder (PTSD) is a highly prevalent mental health disorder. Due to the high level of variability in susceptibility and severity, PTSD therapies are still insufficient. In addition to environmental exposures, genetic risks play a prominent role and one such factor is apolipoprotein E. The protein (apoE) is functionally involved in cholesterol transport and metabolism and exists as 3 major isoforms in humans: E2, E3, and E4. To model the role of apolipoprotein E isoform in stress-related changes in behavior and cognition, female and male mice (3-5 months of age) expressing E2, E3, or E4 were used. Mice were either placed into control groups or exposed to chronic variable stress (CVS), which has been shown to induce PTSD-like behavioral and neuroendocrine changes. E2 mice showed a unique response to CVS compared to E3 and E4 mice that included impaired spatial learning and memory, increased adrenal gland weight, and no increase in glucocorticoid receptor protein levels (normalized to apoE levels). In addition, the cholesterol metabolite 7-ketocholesterol was elevated in the cortex after CVS in E3 and E4, but not E2 female mice. E2 confers unique changes in behavioral, cognitive, and biomarker profiles after stress exposure and identify 7-ketocholesterol as a possible novel biomarker of the traumatic stress response. We further explored the relationship between E2 and PTSD in an understudied population by genotyping 102 patients of Cambodian and Vietnamese ethnicity. E2 carriers demonstrated a higher odds ratio of having a PTSD diagnosis compared to E3/E3 carriers, supporting that the E2 genotype is associated with PTSD diagnosis after trauma exposure in this population.

First case series of Polish patients with cerebrotendinous xanthomatosis and systematic review of cases from the 21st century

Cerebrotendinous xanthomatosis (CTX) is an inborn error of metabolism caused by recessive variants in the cytochrome P450 CYP27A1 gene. CTX is said to manifest with childhood-onset chronic diarrhea and the classic triad of juvenile-onset cataracts, Achilles tendons xanthomas, and progressive ataxia. It is currently one of the few inherited neurometabolic disorders amenable to a specific treatment. The diagnosis may be significantly delayed resulting in permanent neurological impairment. A retrospective review of the clinical characteristics and diagnostic findings in case series of six Polish patients with CTX. Additional retrospective review of symptoms and pathogenic variants of 568 CTX available cases and case series from the past 20 years. To the best of our knowledge, this is the widest review of CTX cases reported in years 2000-2021. We report the largest cohort of Polish patients ever published, with the identification of two hot-spot mutations. During the review of available 568 cases, we found significant differences in the clinical phenotypes and the localization of variants within the gene between Asian and non-Asian populations. These findings may facilitate molecular testing in the Polish and Asian populations. Invariably better screening for CTX and wider awareness is needed.

11β-hydroxysteroid dehydrogenases: A growing multi-tasking family

This review briefly addresses the history of the discovery and elucidation of the three cloned 11β-hydroxysteroid dehydrogenase (11βHSD) enzymes in the human, 11βHSD1, 11βHSD2 and 11βHSD3, an NADP⁺-dependent dehydrogenase also called the 11βHSD1-like dehydrogenase (11βHSD1L), as well as evidence for yet identified 11βHSDs. Attention is devoted to more recently described aspects of this multi-functional family. The importance of 11βHSD substrates other than glucocorticoids including bile acids, 7-keto sterols, neurosteroids, and xenobiotics is discussed, along with examples of pathology when functions of these multi-tasking enzymes are disrupted. 11βHSDs modulate the intracellular concentration of glucocorticoids, thereby regulating the activation of the glucocorticoid and mineralocorticoid receptors, and 7β-27-hydroxycholesterol, an agonist of the retinoid-related orphan receptor gamma (RORγ). Key functions of this nuclear transcription factor include regulation of immune cell differentiation, cytokine production and inflammation at the cell level. 11βHSD1 expression and/or glucocorticoid reductase activity are inappropriately increased with age and in obesity and metabolic syndrome (MetS). Potential causes for disappointing results of the clinical trials of selective inhibitors of 11βHSD1 in the treatment of these disorders are discussed, as well as the potential for more targeted use of inhibitors of 11βHSD1 and 11βHSD2.

Anti-PCSK 9 antibodies increase the ratios of the brain-specific oxysterol 24S-hydroxycholesterol to cholesterol and to 27-hydroxycholesterol in the serum

AIMS

The serum ratios of the brain-specific oxysterol 24S-hydroxycholesterol (24S-OHC) to cholesterol and to 27-OHC reflect brain cholesterol turnover. We studied the effect of proprotein convertase subtilisin/kexin type 9 monoclonal antibodies (PCSK9ab) that enhance low-density lipoprotein receptor activity on serum cholesterol and oxysterol concentrations.

METHODS

Twenty-eight hypercholesterolaemic patients (15 males and 13 females) responding insufficiently to maximally tolerated statin and/or ezetimibe therapy were additionally subcutanously treated biweekly with either the PCSK9ab alirocumab (150 mg, n = 13) or evolocumab (140 mg, n = 15). Fasting serum cholesterol was measured by gas chromatography and the oxysterols 24S-OHC and 27-OHC using gas chromatography-mass spectrometry before, after 1-month (n = 28) and after 3-month (n = 13) treatment.

RESULTS

As expected, PCSK9ab treatment lowered serum cholesterol and oxysterol levels after 1 month. The serum ratio of 24S-OHC to cholesterol increased after 1 month by 17 ± 28% (mean ± standard deviation; 95% confidence interval [CI]: 5.8 to 28%; P < .01) and 24S-OHC to 27-OHC by 15 ± 39% (95% CI: 0.2 to 30%; P < .01). Within 3 months, 24S-OHC to cholesterol increased by 2.8 μg g^-1 mo^-1 (95% CI: 2.1 to 3.6; P < .01) and 24S-OHC to 27-OHC by 0.019 mo^-1 (95% CI: 0.007 to 0.032; P < .01).

CONCLUSION

The serum ratios of 24S-OHC to cholesterol and to 27-OHC increased after treatment with PCSK9ab. We hypothesize that this is caused by a reduced entrance of 27-OHC into the brain, increased synthesis of brain cholesterol, increased production of 24S-OHC and its secretion across the blood-brain barrier.

Electrophilic oxysterols: generation, measurement and protein modification

Cholesterol is an essential component of mammalian plasma membranes. Alterations in sterol metabolism or oxidation have been linked to various pathological conditions, including cardiovascular diseases, cancer, and neurodegenerative disorders. Unsaturated sterols are vulnerable to oxidation induced by singlet oxygen and other reactive oxygen species. This process yields reactive sterol oxidation products, including hydroperoxides, epoxides as well as aldehydes. These oxysterols, in particular those with high electrophilicity, can modify nucleophilic sites in biomolecules and affect many cellular functions. Here, we review the generation and measurement of reactive sterol oxidation products with emphasis on cholesterol hydroperoxides and aldehyde derivatives (electrophilic oxysterols) and their effects on protein modifications.

A Comprehensive Review on Oxysterols and Related Diseases

The present review aims to provide a complete and comprehensive summary of current literature relevant to oxysterols and related diseases. Oxidation of cholesterol leads to the formation of a large number of oxidized products, generally known as oxysterols. They are intermediates in the biosynthesis of bile acids, steroid hormones, and 1,25- dihydroxyvitamin D3. Although oxysterols are considered as metabolic intermediates, there is a growing body of evidence that many of them are bioactive, and their absence or excess may be part of the cause of a disease phenotype. These compounds derive from either enzymatic or non-enzymatic oxidation of cholesterol. This study provides comprehensive information about the structures, formation, and types of oxysterols even when involved in certain disease states, focusing on their effects on metabolism and linkages with these diseases. The role of specific oxysterols as mediators in various disorders, such as degenerative (age-related) and cancer-related disorders, has now become clearer. Oxysterol levels may be employed as suitable markers for the diagnosis of specific diseases or in predicting the incidence rate of diseases, such as diabetes mellitus, Alzheimer's disease, multiple sclerosis, osteoporosis, lung cancer, breast cancer, and infertility. However, further investigations may be required to confirm these mentioned possibilities.

Cholesterol metabolism pathways - are the intermediates more important than the products?

Every cell in vertebrates possesses the machinery to synthesise cholesterol and to metabolise it. The major route of cholesterol metabolism is conversion to bile acids. Bile acids themselves are interesting molecules being ligands to nuclear and G protein‐coupled receptors, but perhaps the intermediates in the bile acid biosynthesis pathways are even more interesting and equally important. Here, we discuss the biological activity of the different intermediates generated in the various bile acid biosynthesis pathways. We put forward the hypothesis that the acidic pathway of bile acid biosynthesis has primary evolved to generate signalling molecules and its utilisation by hepatocytes provides an added bonus of producing bile acids to aid absorption of lipids in the intestine.

Oxiapoptophagy: A type of cell death induced by some oxysterols

Oxysterols are oxidized forms of cholesterol generated from cholesterol by auto-oxidation, enzymatic processes, or both. Some of them (7-ketocholesterol, 7β-hydroxycholesterol and 24(S)-hydroxycholesterol), when used at cytotoxic concentrations on different cell types from different species (mesenchymal bone marrow cells, monocytic cells and nerve cells), induce a type of cell death associated with OXIdative stress and several characteristics of APOPTOsis and autoPHAGY, defined as oxiapoptophagy. Oxidative stress is associated with overproduction of ROS, increased antioxidant enzyme activities, lipid peroxidation and protein carbonylation. Apoptosis is associated with activation of the mitochondrial pathway, opening of the mitochondrial permeability pore, loss of mitochondrial membrane potential, caspase-3 activation, PARP degradation, nuclear condensation and/or fragmentation. Autophagy is characterized by autophagic vacuoles revealed by monodansylcadaverine staining and transmission electron microscopy, plus increased ratio of LC-3II/LC-3I. In addition, morphological, topographical and functional changes of the peroxisome are observed. 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.

Localization of sterols and oxysterols in mouse brain reveals distinct spatial cholesterol metabolism

The brain is a remarkably complex organ and cholesterol homeostasis underpins brain function. It is known that cholesterol is not evenly distributed across different brain regions; however, the precise map of cholesterol metabolism in the brain remains unclear. If cholesterol metabolism is to be correlated with brain function it is essential to generate such a map. Here we describe an advanced mass spectrometry platform to reveal spatial cholesterol metabolism in situ at 400-µm spot diameter on 10-µm tissue slices from mouse brain. We mapped, not only cholesterol, but also other biologically active sterols arising from cholesterol turnover in both wild type and mice lacking cholesterol 24S-hydroxylase (CYP46A1), the major cholesterol metabolizing enzyme.

Dysregulated cholesterol metabolism is implicated in a number of neurological disorders. Many sterols, including cholesterol and its precursors and metabolites, are biologically active and important for proper brain function. However, spatial cholesterol metabolism in brain and the resulting sterol distributions are poorly defined. To better understand cholesterol metabolism in situ across the complex functional regions of brain, we have developed on-tissue enzyme-assisted derivatization in combination with microliquid extraction for surface analysis and liquid chromatography-mass spectrometry to locate sterols in tissue slices (10 µm) of mouse brain. The method provides sterolomic analysis at 400-µm spot diameter with a limit of quantification of 0.01 ng/mm². It overcomes the limitations of previous mass spectrometry imaging techniques in analysis of low-abundance and difficult-to-ionize sterol molecules, allowing isomer differentiation and structure identification. Here we demonstrate the spatial distribution and quantification of multiple sterols involved in cholesterol metabolic pathways in wild-type and cholesterol 24S-hydroxylase knockout mouse brain. The technology described provides a powerful tool for future studies of spatial cholesterol metabolism in healthy and diseased tissues.

Metabolism of Non-Enzymatically Derived Oxysterols: Clues from sterol metabolic disorders

Cholestane-3β,5α,6β-triol (3β,5α,6β-triol) is formed from cholestan-5,6-epoxide (5,6-EC) in a reaction catalysed by cholesterol epoxide hydrolase, following formation of 5,6-EC through free radical oxidation of cholesterol. 7-Oxocholesterol (7-OC) and 7β-hydroxycholesterol (7β-HC) can also be formed by free radical oxidation of cholesterol. Here we investigate how 3β,5α,6β-triol, 7-OC and 7β-HC are metabolised to bile acids. We show, by monitoring oxysterol metabolites in plasma samples rich in 3β,5α,6β-triol, 7-OC and 7β-HC, that these three oxysterols fall into novel branches of the acidic pathway of bile acid biosynthesis becoming (25R)26-hydroxylated then carboxylated, 24-hydroxylated and side-chain shortened to give the final products 3β,5α,6β-trihydroxycholanoic, 3β-hydroxy-7-oxochol-5-enoic and 3β,7β-dihydroxychol-5-enoic acids, respectively. The intermediates in these pathways may be causative of some phenotypical features of, and/or have diagnostic value for, the lysosomal storage diseases, Niemann Pick types C and B and lysosomal acid lipase deficiency. Free radical derived oxysterols are metabolised in human to unusual bile acids via novel branches of the acidic pathway, intermediates in these pathways are observed in plasma.

The acidic pathway of bile acid synthesis: Not just an alternative pathway☆

Over the last two decades, the prevalence of obesity, and metabolic syndromes (MS) such as non-alcoholic fatty liver disease (NAFLD) and type 2 diabetes mellitus (T2DM), have dramatically increased. Bile acids play a major role in the digestion, absorption of nutrients, and the body's redistribution of absorbed lipids as a function of their chemistry and signaling properties. As a result, a renewed interest has developed in the bile acid metabolic pathways with the challenge of gaining insight into novel treatment approaches for this rapidly growing healthcare problem. Of the two major pathways of bile acid synthesis in the liver, the foremost role of the acidic (alternative) pathway is to generate and control the levels of regulatory oxysterols that help control cellular cholesterol and lipid homeostasis. Cholesterol transport to mitochondrial sterol 27-hydroxylase (CYP27A1) by steroidogenic acute regulatory protein (StarD1), and the subsequent 7α-hydroxylation of oxysterols by oxysterol 7α-hydroxylase (CYP7B1) are the key regulatory steps of the pathway. Recent observations suggest CYP7B1 to be the ultimate controller of cellular oxysterol levels. This review discusses the acidic pathway and its contribution to lipid, cholesterol, carbohydrate, and energy homeostasis. Additionally, discussed is how the acidic pathway's dysregulation not only leads to a loss in its ability to control cellular cholesterol and lipid homeostasis, but leads to inflammatory conditions.

Squalene Epoxidase Correlates E-Cadherin Expression and Overall Survival in Colorectal Cancer Patients: The Impact on Prognosis and Correlation to Clinicopathologic Features

Squalene epoxidase (SE), coded by SQLE, is an important rate-limiting enzyme in the cholesterol biosynthetic pathway. Recently, the aberrant expression of SQLE, which is responsible for epithelial to mesenchymal transition (EMT), has been reported in various types of cancer. This study was undertaken to clarify the clinicopathologic implications of SE in patients with stage I to IV colorectal cancer (CRC). We also analyzed the expression patterns of SE in association with E-cadherin in a series of CRCs. We detected the cytoplasmic expression of SE in 59.4% of carcinoma samples by immunohistochemistry (IHC). There was a significant correlation between a high level of SE expression and lymphovascular (LV) invasion (p < 0.001), tumor budding (p < 0.001), invasion depth (p = 0.002), regional lymph node metastasis (p < 0.001), and pathologic TNM stage (p < 0.001). SE is more abundantly expressed at the invasive front, and reversely correlated with E-cadherin expression. Patients with SE-positive CRC had shorter recurrence-free survival (RFS) and poor overall survival (OS) than those with SE-negative CRC in multivariate analysis (p < 0.001 and p < 0.001, respectively). These data suggest that SE can serve as a valuable biomarker for unfavorable prognosis, and as a possible therapeutic target in CRCs.

Mitochondrial oxysterol biosynthetic pathway gives evidence for CYP7B1 as controller of regulatory oxysterols

The aim of this paper was to more completely study the mitochondrial CYP27A1 initiated acidic pathway of cholesterol metabolism. The mitochondrial CYP27A1 initiated pathway of cholesterol metabolism (acidic pathway) is known to synthesize two well-described vital regulators of cholesterol/lipid homeostasis, (25R)-26-hydroxycholesterol (26HC) and 25-hydroxycholesterol (25HC). Both 26HC and 25HC have been shown to be subsequently 7α-hydroxylated by Cyp7b1; reducing their regulatory abilities and furthering their metabolism to chenodeoxycholic acid (CDCA). Cholesterol delivery into the inner mitochondria membrane, where CYP27A1 is located, is considered the pathway's only rate-limiting step. To further explore the pathway, we increased cholesterol transport into mitochondrial CYP27A1 by selectively increased expression of the gene encoding the steroidogenic acute transport protein (StarD1). StarD1 overexpression led to an unanticipated marked down-regulation of oxysterol 7α-hydroxylase (Cyp7b1), a marked increase in 26HC, and the formation of a third vital regulatory oxysterol, 24(S)-hydroxycholesterol (24HC), in B6/129 mice livers. To explore the further metabolism of 24HC, as well as, 25HC and 26HC, characterizations of oxysterols and bile acids using three murine models (StarD1 overexpression, Cyp7b1^-/-, Cyp27a1^-/-) and human Hep G2 cells were conducted. This report describes the discovery of a new mitochondrial-initiated pathway of oxysterol/bile acid biosynthesis. Just as importantly, it provides evidence for CYP7B1 as a key regulator of three vital intracellular regulatory oxysterol levels.

Developing an Enzyme-Assisted Derivatization Method for Analysis of C27 Bile Alcohols and Acids by Electrospray Ionization-Mass Spectrometry

Enzyme-assisted derivatization for sterol analysis (EADSA) is a technology designed to enhance sensitivity and specificity for sterol analysis using electrospray ionization⁻mass spectrometry. To date it has only been exploited on sterols with a 3β-hydroxy-5-ene or 3β-hydroxy-5α-hydrogen structure, using bacterial cholesterol oxidase enzyme to convert the 3β-hydroxy group to a 3-oxo group for subsequent derivatization with the positively charged Girard hydrazine reagents, or on substrates with a native oxo group. Here we describe an extension of the technology by substituting 3α-hydroxysteroid dehydrogenase (3α-HSD) for cholesterol oxidase, making the method applicable to sterols with a 3α-hydroxy-5β-hydrogen structure. The 3α-HSD enzyme works efficiently on bile alcohols and bile acids with this stereochemistry. However, as found by others, derivatization of the resultant 3-oxo group with a hydrazine reagent does not go to completion in the absence of a conjugating double bond in the sterol structure. Nevertheless, Girard P derivatives of bile alcohols and C₂₇ acids give an intense molecular ion ([M]⁺) upon electrospray ionization and informative fragmentation spectra. The method shows promise for analysis of bile alcohols and 3α-hydroxy-5β-C₂₇-acids, enhancing the range of sterols that can be analyzed at high sensitivity in sterolomic studies.

The promiscuous estrogen receptor: Evolution of physiological estrogens and response to phytochemicals and endocrine disruptors

Many actions of estradiol (E2), the principal physiological estrogen in vertebrates, are mediated by estrogen receptor-α (ERα) and ERβ. An important physiological feature of vertebrate ERs is their promiscuous response to several physiological steroids, including estradiol (E2), Δ⁵-androstenediol, 5α-androstanediol, and 27-hydroxycholesterol. A novel structural characteristic of Δ⁵-androstenediol, 5α-androstanediol, and 27-hydroxycholesterol is the presence of a C19 methyl group, which precludes the presence of an aromatic A ring with a C3 phenolic group that is a defining property of E2. The structural diversity of these estrogens can explain the response of the ER to synthetic chemicals such as bisphenol A and DDT, which disrupt estrogen physiology in vertebrates, and the estrogenic activity of a variety of plant-derived chemicals such as genistein, coumestrol, and resveratrol. Diversity in the A ring of physiological estrogens also expands potential structures of industrial chemicals that can act as endocrine disruptors. Compared to E2, synthesis of 27-hydroxycholesterol and Δ⁵-androstenediol is simpler, leading us, based on parsimony, to propose that one or both of these steroids or a related metabolite was a physiological estrogen early in the evolution of the ER, with E2 assuming this role later as the canonical estrogen. In addition to the well-studied role of the ER in reproductive physiology, the ER also is an important transcription factor in non-reproductive tissues such as the cardiovascular system, kidney, bone, and brain. Some of these ER actions in non-reproductive tissues appeared early in vertebrate evolution, long before the emergence of mammals.

Identification of unusual oxysterols and bile acids with 7-oxo or 3β,5α,6β-trihydroxy functions in human plasma by charge-tagging mass spectrometry with multistage fragmentation

7-Oxocholesterol (7-OC), 5,6-epoxycholesterol (5,6-EC), and its hydrolysis product cholestane-3β,5α,6β-triol (3β,5α,6β-triol) are normally minor oxysterols in human samples; however, in disease, their levels may be greatly elevated. This is the case in plasma from patients suffering from some lysosomal storage disorders, e.g., Niemann-Pick disease type C, or the inborn errors of sterol metabolism, e.g., Smith-Lemli-Opitz syndrome and cerebrotendinous xanthomatosis. A complication in the analysis of 7-OC and 5,6-EC is that they can also be formed ex vivo from cholesterol during sample handling in air, causing confusion with molecules formed in vivo. When formed endogenously, 7-OC, 5,6-EC, and 3β,5α,6β-triol can be converted to bile acids. Here, we describe methodology based on chemical derivatization and LC/MS with multistage fragmentation (MSⁿ) to identify the necessary intermediates in the conversion of 7-OC to 3β-hydroxy-7-oxochol-5-enoic acid and 5,6-EC and 3β,5α,6β-triol to 3β,5α,6β-trihydroxycholanoic acid. Identification of intermediate metabolites is facilitated by their unusual MSⁿ fragmentation patterns. Semiquantitative measurements are possible, but absolute values await the synthesis of isotope-labeled standards.

27-hydroxycholesterol: A novel player in molecular carcinogenesis of breast and prostate cancer

Several studies have suggested an etiological role for hypercholesterolemia in the pathogenesis of breast cancer and prostate cancer (PCa). However, the molecular mechanisms that underlie and mediate the hypercholesterolemia-fostered increased risk for breast cancer and PCa are yet to be determined. The discovery that the most abundant cholesterol oxidized metabolite in the plasma, 27 hydroxycholesterol (27-OHC), is a selective estrogen receptor modulator (SERM) and an agonist of Liver X receptors (LXR) partially fills the void in our understanding and knowledge of the mechanisms that may link hypercholesterolemia to development and progression of breast cancer and PCa. The wide spectrum and repertoire of SERM and LXR-dependent effects of 27-OHC in the context of all facets and aspects of breast cancer and prostate cancer biology are reviewed in this manuscript in a very comprehensive manner. This review highlights recent findings pertaining to the role of 27-OHC in breast cancer and PCa and delineates the signaling mechanisms involved in the governing of different facets of tumor biology, that include tumor cell proliferation, epithelial-mesenchymal transition (EMT), as well as tumor cell invasion, migration, and metastasis. We also discuss the limitations of contemporary studies and lack of our comprehension of the entire gamut of effects exerted by 27-OHC that may be relevant to the pathogenesis of breast cancer and PCa. We unveil and propose potential future directions of research that may further our understanding of the role of 27-OHC in breast cancer and PCa and help design therapeutic interventions against endocrine therapy-resistant breast cancer and PCa.

The cholesterol metabolite 27-hydroxycholesterol stimulates cell proliferation via ERβ in prostate cancer cells

BACKGROUND

For every six men, one will be diagnosed with prostate cancer (PCa) in their lifetime. Estrogen receptors (ERs) are known to play a role in prostate carcinogenesis. However, it is unclear whether the estrogenic effects are mediated by estrogen receptor α (ERα) or estrogen receptor β (ERβ). Although it is speculated that ERα is associated with harmful effects on PCa, the role of ERβ in PCa is still ill-defined. The cholesterol oxidized metabolite 27-hydroxycholesterol (27-OHC) has been found to bind to ERs and act as a selective ER modulator (SERM). Increased 27-OHC levels are found in individuals with hypercholesterolemia, a condition that is suggested to be a risk factor for PCa.

METHODS

In the present study, we determined the extent to which 27-OHC causes deleterious effects in the non-tumorigenic RWPE-1, the low tumorigenic LNCaP, and the highly tumorigenic PC3 prostate cancer cells. We conducted cell metabolic activity and proliferation assays using MTS and CyQUANT dyes, protein expression analyses via immunoblots and gene expression analyses via RT-PCR. Additionally, immunocytochemistry and invasion assays were performed to analyze intracellular protein distribution and quantify transepithelial cell motility.

RESULTS

We found that incubation of LNCaP and PC3 cells with 27-OHC significantly increased cell proliferation. We also demonstrate that the ER inhibitor ICI 182,780 (fulvestrant) significantly reduced 27-OH-induced cell proliferation, indicating the involvement of ERs in proliferation. Interestingly, ERβ levels, and to a lesser extent ERα, were significantly increased following incubation of PCa cells with 27-OHC. Furthermore, in the presence of the ERβ specific inhibitor, PHTPP, 27-OHC-induced proliferation is attenuated.

CONCLUSIONS

Altogether, our results show for the first time that 27-OHC, through ER activation, triggers deleterious effect in prostate cancer cell lines. We propose that dysregulated levels of 27-OHC may trigger or exacerbate prostate cancer via acting on ERβ.

Characterization of cholesterol homeostasis in sphingosine-1-phosphate lyase-deficient fibroblasts reveals a Niemann-Pick disease type C-like phenotype with enhanced lysosomal Ca2+ storage

Sphingosine-1-phosphate (S1P) lyase irreversibly cleaves S1P, thereby catalysing the ultimate step of sphingolipid degradation. We show here that embryonic fibroblasts from S1P lyase-deficient mice (Sgpl1^−/−-MEFs), in which S1P and sphingosine accumulate, have features of Niemann-Pick disease type C (NPC) cells. In the presence of serum, overall cholesterol content was elevated in Sgpl1^−/−-MEFs, due to upregulation of the LDL receptor and enhanced cholesterol uptake. Despite this, activation of sterol regulatory element-binding protein-2 was increased in Sgpl1^−/−-MEFs, indicating a local lack of cholesterol at the ER. Indeed, free cholesterol was retained in NPC1-containing vesicles, which is a hallmark of NPC. Furthermore, upregulation of amyloid precursor protein in Sgpl1^−/−-MEFs was mimicked by an NPC1 inhibitor in Sgpl1^+/+-MEFs and reduced by overexpression of NPC1. Lysosomal pH was not altered by S1P lyase deficiency, similar to NPC. Interestingly, lysosomal Ca²⁺ content and bafilomycin A1-induced [Ca²⁺]_i increases were enhanced in Sgpl1^−/−-MEFs, contrary to NPC. These results show that both a primary defect in cholesterol trafficking and S1P lyase deficiency cause overlapping phenotypic alterations, and challenge the present view on the role of sphingosine in lysosomal Ca²⁺ homeostasis.

Cholesterolomics: An update

Cholesterolomics can be regarded as the identification and quantification of cholesterol, its precursors post squalene, and metabolites of cholesterol and of its precursors, in a biological sample. These molecules include 1,25-dihydroxyvitamin D₃, steroid hormones and bile acids and intermediates in their respective biosynthetic pathways. In this short article we will concentrate our attention on intermediates in bile acid biosynthesis pathways, in particular oxysterols and cholestenoic acids. These molecular classes are implicated in the aetiology of a diverse array of diseases including autoimmune disease, Parkinson's disease, motor neuron disease, breast cancer, the lysosomal storage disease Niemann-Pick type C and the autosomal recessive disorder Smith-Lemli-Opitz syndrome. Mass spectrometry (MS) is the dominant technology for sterol analysis including both gas-chromatography (GC)-MS and liquid chromatography (LC)-MS and more recently matrix-assisted laser desorption/ionisation (MALDI)-MS for tissue imaging studies. Here we will discuss exciting biological findings and recent analytical improvements.

p-TsOH-Catalyzed one-pot transformation of di- and trihydroxy steroids towards diverse A/B-ring oxo-functionalization

A milder, facile, and greener transformative protocol, specifically on solid supports, to yield A-ring and/or B-ring oxo-functionalized steroids has been accomplished.

Reduced Plasma Levels of 25-Hydroxycholesterol and Increased Cerebrospinal Fluid Levels of Bile Acid Precursors in Multiple Sclerosis Patients

Multiple sclerosis (MS) is an autoimmune, inflammatory disease of the central nervous system (CNS). We have measured the levels of over 20 non-esterified sterols in plasma and cerebrospinal fluid (CSF) from patients suffering from MS, inflammatory CNS disease, neurodegenerative disease and control patients. Analysis was performed following enzyme-assisted derivatisation by liquid chromatography–mass spectrometry (LC–MS) exploiting multistage fragmentation (MSⁿ). We found increased concentrations of bile acid precursors in CSF from each of the disease states and that patients with inflammatory CNS disease classified as suspected autoimmune disease or of unknown aetiology also showed elevated concentrations of 25-hydroxycholestertol (25-HC, P < 0.05) in CSF. Cholesterol concentrations in CSF were not changed except for patients diagnosed with amyotrophic lateral sclerosis (P < 0.01) or pathogen-based infections of the CNS (P < 0.05) where they were elevated. In plasma, we found that 25-HC (P < 0.01), (25R)26-hydroxycholesterol ((25R)26-HC, P < 0.05) and 7α-hydroxy-3-oxocholest-4-enoic acid (7αH,3O-CA, P < 0.05) were reduced in relapsing-remitting MS (RRMS) patients compared to controls. The pattern of reduced plasma levels of 25-HC, (25R)26-HC and 7αH,3O-CA was unique to RRMS. In summary, in plasma, we find that the concentration of 25-HC in RRMS patients is significantly lower than in controls. This is consistent with the hypothesis that a lower propensity of macrophages to synthesise 25-HC will result in reduced negative feedback by 25-HC on IL-1 family cytokine production and exacerbated MS. In CSF, we find that the dominating metabolites reflect the acidic pathway of bile acid biosynthesis and the elevated levels of these in CNS disease is likely to reflect cholesterol release as a result of demyelination or neuronal death. 25-HC is elevated in patients with inflammatory CNS disease probably as a consequence of up-regulation of the type 1 interferon-stimulated gene cholesterol 25-hydroxylase in macrophages.

Defective cholesterol metabolism in amyotrophic lateral sclerosis

As neurons die, cholesterol is released in the central nervous system (CNS); hence, this sterol and its metabolites may represent a biomarker of neurodegeneration, including in amyotrophic lateral sclerosis (ALS), in which altered cholesterol levels have been linked to prognosis. More than 40 different sterols were quantified in serum and cerebrospinal fluid (CSF) from ALS patients and healthy controls. In CSF, the concentration of cholesterol was found to be elevated in ALS samples. When CSF metabolite levels were normalized to cholesterol, the cholesterol metabolite 3β,7α-dihydroxycholest-5-en-26-oic acid, along with its precursor 3β-hydroxycholest-5-en-26-oic acid and product 7α-hydroxy-3-oxocholest-4-en-26-oic acid, were reduced in concentration, whereas metabolites known to be imported from the circulation into the CNS were not found to differ in concentration between groups. Analysis of serum revealed that (25R)26-hydroxycholesterol, the immediate precursor of 3β-hydroxycholest-5-en-26-oic acid, was reduced in concentration in ALS patients compared with controls. We conclude that the acidic branch of bile acid biosynthesis, known to be operative in-part in the brain, is defective in ALS, leading to a failure of the CNS to remove excess cholesterol, which may be toxic to neuronal cells, compounded by a reduction in neuroprotective 3β,7α-dihydroxycholest-5-en-26-oic acid.

Ozone-derived Oxysterols Affect Liver X Receptor (LXR) Signaling: A POTENTIAL ROLE FOR LIPID-PROTEIN ADDUCTS

When inhaled, ozone (O₃) interacts with cholesterols of airway epithelial cell membranes or the lung-lining fluid, generating chemically reactive oxysterols. The mechanism by which O₃-derived oxysterols affect molecular function is unknown. Our data show that in vitro exposure of human bronchial epithelial cells to O₃ results in the formation of oxysterols, epoxycholesterol-α and -β and secosterol A and B (Seco A and Seco B), in cell lysates and apical washes. Similarly, bronchoalveolar lavage fluid obtained from human volunteers exposed to O₃ contained elevated levels of these oxysterol species. As expected, O₃-derived oxysterols have a pro-inflammatory effect and increase NF-κB activity. Interestingly, expression of the cholesterol efflux pump ATP-binding cassette transporter 1 (ABCA1), which is regulated by activation of the liver X receptor (LXR), was suppressed in epithelial cells exposed to O₃ Additionally, exposure of LXR knock-out mice to O₃ enhanced pro-inflammatory cytokine production in the lung, suggesting LXR inhibits O₃-induced inflammation. Using alkynyl surrogates of O₃-derived oxysterols, our data demonstrate adduction of LXR with Seco A. Similarly, supplementation of epithelial cells with alkynyl-tagged cholesterol followed by O₃ exposure causes observable lipid-LXR adduct formation. Experiments using Seco A and the LXR agonist T0901317 (T09) showed reduced expression of ABCA1 as compared with stimulation with T0901317 alone, indicating that Seco A-LXR protein adduct formation inhibits LXR activation by traditional agonists. Overall, these data demonstrate that O₃-derived oxysterols have pro-inflammatory functions and form lipid-protein adducts with LXR, thus leading to suppressed cholesterol regulatory gene expression and providing a biochemical mechanism mediating O₃-derived formation of oxidized lipids in the airways and subsequent adverse health effects.

Neuroendocrine Regulation of Metabolism

Given the current environment in most developed countries, it is a challenge to maintain a good balance between calories consumed and calories burned, although maintenance of metabolic balance is key to good health. Therefore, understanding how metabolic regulation is achieved and how the dysregulation of metabolism affects health is an area of intense research. Most studies focus on the hypothalamus, which is a brain area that acts as a key regulator of metabolism. Among the nuclei that comprise the hypothalamus, the arcuate nucleus is one of the major mediators in the regulation of food intake. The regulation of energy balance is also a key factor ensuring the maintenance of any species as a result of the dependence of reproduction on energy stores. Adequate levels of energy reserves are necessary for the proper functioning of the hypothalamic-pituitary-gonadal axis. This review discusses valuable data presented in the 2015 edition of the International Workshop of Neuroendocrinology concerning the fundamental nature of the hormonal regulation of the hypothalamus and the impact on energy balance and reproduction.

Oxysterols and mechanisms of survival signaling

Oxysterols, a family of oxidation products of cholesterol, are increasingly drawing attention of scientists to their multifaceted biochemical properties, several of them of clear relevance to human pathophysiology. Taken up by cells through both vesicular and non-vesicular ways or often generated intracellularly, oxysterols contribute to modulate not only the inflammatory and immunological response but also cell viability, metabolism and function by modulating several signaling pathways. Moreover, they have been recognized as elective ligands for the most important nuclear receptors. The outcome of such a complex network of intracellular reactions promoted by these cholesterol oxidation products appears to be largely dependent not only on the type of cells, the dynamic conditions of the cellular and tissue environment but also on the concentration of the oxysterols. Here focus has been given to the cascade of molecular events exerted by relatively low concentrations of certain oxysterols that elicit survival and functional signals in the cells, with the aim to contribute to further expand the knowledge about the biological and physiological potential of the biochemical reactions triggered and modulated by oxysterols.

Oxysterols: Synthesis and anti-leishmanial activities

Oxygenated sterols (2-16) were synthesized by skeletal rearrangement of steroidal allylic alcohols. All the derivatives were screened for their anti-leishmanial activities. Compounds 3, 11 and 12 showed potent activities. Compound 12 was found least toxic and induced highest nitric oxide (NO) at 48 h. Least toxicity of compound 12 on splenocytes validated its best anti-amastigote effect and induction of NO.

Cholestane-3β,5α,6β-triol: high levels in Niemann-Pick type C, cerebrotendinous xanthomatosis, and lysosomal acid lipase deficiency

Niemann-Pick type C (NPC) is a progressive neurodegenerative disease characterized by lysosomal/endosomal accumulation of unesterified cholesterol and glycolipids. Recent studies have shown that plasma cholestane-3β,5α,6β-triol (CT) and 7-ketocholesterol (7-KC) could be potential biomarkers for the diagnosis of NPC patients. We aimed to know the sensitivity and specificity of these biomarkers for the diagnosis of NPC compared with other diseases that can potentially lead to oxysterol alterations. We studied 107 controls and 122 patients including 16 with NPC, 3 with lysosomal acid lipase (LAL) deficiency, 8 with other lysosomal diseases, 5 with galactosemia, 11 with cerebrotendinous xanthomatosis (CTX), 3 with Smith-Lemli-Opitz, 14 with peroxisomal biogenesis disorders, 19 with unspecific hepatic diseases, 13 with familial hypercholesterolemia, and 30 with neurological involvement and no evidence of an inherited metabolic disease. CT and 7-KC were analyzed by HPLC-ESI-MS/MS as mono-dimethylglycine derivatives. Levels of 7-KC were high in most of the studied diseases, whereas those of CT were only high in NPC, LAL, and CTX patients. Consequently, although CT is a sensitive biomarker of NPC disease, including those cases with doubtful filipin staining, it is not specific. 7-KC is a very unspecific biomarker.

Validation of an isotope dilution gas chromatography-mass spectrometry method for combined analysis of oxysterols and oxyphytosterols in serum samples

We describe the validation of a method for the analysis of oxysterols, i.e. oxycholesterols and oxyphytosterols, in human serum using gas chromatography-mass spectrometry selected ion monitoring (GC-MS-SIM). Concentrations of 7α- and 7β-hydroxy-, and 7oxo-cholesterol, -campesterol, and -sitosterol as well as 4β-hydroxycholesterol and side-chain oxygenated 24S-, 25-, and 27-hydroxycholesterol were determined by isotope dilution methodology. After saponification at room temperature the oxysterols were extracted, separated from their substrates, cholesterol, campesterol, and sitosterol, by solid phase extraction, and subsequently derivatised to their corresponding trimethylsilyl-ethers prior to GC-MS-SIM. In order to prevent artificial autoxidation butylated hydroxytoluene and ethylenediaminetetraacetic acid were added. The validation of the method was performed according to the International Conference on Harmonisation guidance, including limits of detection and quantification, ranges, recovery and precision. Due to improved instrumental settings and work-up procedure, limits of detection and quantification ranged between 8.0-202.0pg/mL and 28.0-674pg/mL, respectively. Recovery data in five calibration points varied between 91.9% and 116.8% and in serum samples between 93.1% and 118.1%. The mean coefficient of variation (CV) for the recovery of all compounds was <10%. Well satisfying CVs for within-day precision (2.1-10.8%) and for between-day precision (2.3-12.1%) were obtained. More than 20 samples could be processed in a single routine day and test series of about 300 samples can be realised without impairment of the validation parameters during a sequence. Comparison of oxysterol and oxyphytosterol content in serum and plasma revealed no difference. A fully validated isotope dilution methodology for the quantification of oxycholesterols and oxyphytosterols from human serum or plasma is presented.

Cholesterol under oxidative stress-How lipid membranes sense oxidation as cholesterol is being replaced by oxysterols

The behavior of oxysterols in phospholipid membranes and their effects on membrane properties were investigated by means of dynamic light scattering, fluorescence spectroscopy, NMR, and extensive atomistic simulations. Two families of oxysterols were scrutinized-tail-oxidized sterols, which are mostly produced by enzymatic processes, and ring-oxidized sterols, formed mostly via reactions with free radicals. The former family of sterols was found to behave similar to cholesterol in terms of molecular orientation, roughly parallel to the bilayer normal, leading to increasing membrane stiffness and suppression of its membrane permeability. In contrast, ring-oxidized sterols behave quantitatively differently from cholesterol. They acquire tilted orientations and therefore disrupt the bilayer structure with potential implications for signaling and other biochemical processes in the membranes.

Detection of dihydroxycholesterols in human plasma using HPLC-ESI-MS/MS

We report a straightforward sample preparation procedure and a direct liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) method for the analysis of 7alpha,25-dihydroxycholesterol (7α25-OHC) and 7alpha,27-dihydroxycholesterol (7α27-OHC). By applying a slow protein precipitation approach using cold ethanol, we were able to detect and quantify 7α25-OHC and 7α27-OHC in a fast and reliable manner. The average concentrations from 20 healthy individuals were determined to be 0.21±0.05nM for 7α25-OHC and 3.4±0.1nM for 7α27-OHC. In addition, we are the first to report the average degrees of esterification (n=8) to be 73.8% and 82% for 7α25-OHC and 7α27-OHC, respectively. Using the established method, we achieved the sensitivity sufficient for detecting low abundant dihydroxylated oxysterols in healthy individuals. This result should enable extension of these studies towards a comprehensive analysis of oxysterol levels under disease conditions.

Cholesterol metabolites exported from human brain

The human brain contains approximately 25% of the body's cholesterol. The brain is separated from the circulation by the blood brain barrier. While cholesterol will not passes this barrier, oxygenated forms of cholesterol can cross the barrier. Here by measuring the difference in the oxysterol content of blood plasma in the jugular vein and in a forearm vein by mass spectrometry (MS) we were able to determine the flux of more than 20 cholesterol metabolites between brain and the circulation. We confirm that 24S-hydroxycholesterol is exported from brain at a rate of about 2-3mg/24h. Gas chromatography (GC)-MS data shows that the cholesterol metabolites 5α-hydroxy-6-oxocholesterol (3β,5α-dihydroxycholestan-6-one), 7β-hydroxycholesterol and 7-oxocholesterol, generally considered to be formed through reactive oxygen species, are similarly exported from brain at rates of about 0.1, 2 and 2mg/24h, respectively. Although not to statistical significance both GC-MS and liquid chromatography (LC)-MS methods indicate that (25R)26-hydroxycholesterol is imported to brain, while LC-MS indicates that 7α-hydroxy-3-oxocholest-4-enoic acid is exported from brain.

Liver X receptors and cholesterol metabolism: role in ventral midbrain development and neurodegeneration

The development of the ventral midbrain is orchestrated by a number of cell-extrinsic and -intrinsic factors that control critical processes, such as the patterning of the neural tube along the main body axis and the specification of diverse neuronal cell types in distinct positions of the neural tube. Subsequently, the regulation of neurogenesis and survival— acquire particular relevance in order to define the final size of diverse neuronal populations. In a series of studies during the last few years, we have identified liver X receptors (LXRs) as critical regulators of ventral midbrain development. Moreover, specific cholesterol derivatives present in the midbrain or in the cerebrospinal fluid were identified as LXR ligands, capable of specifically and selectively regulating neurogenesis and the survival of distinct neuronal populations, including midbrain dopamine neurons. These studies have shown that cholesterol derivatives are an entirely new class of factors capable of regulating both neuronal survival and neurogenesis, thus providing a direct link between cholesterol metabolism and brain development. In addition, LXRs and cholesterol metabolism were found to play a critical role in regulating the balance between neuronal survival and death in diverse midbrain neuronal populations. In this review, we will focus on these two aspects and on the possible role of cholesterol metabolism and LXRs in neurodegeneration.

Electrochemical oxidation of cholesterol

Indirect cholesterol electrochemical oxidation in the presence of various mediators leads to electrophilic addition to the double bond, oxidation at the allylic position, oxidation of the hydroxy group, or functionalization of the side chain. Recent studies have proven that direct electrochemical oxidation of cholesterol is also possible and affords different products depending on the reaction conditions.

Human native, enzymatically modified and oxidized low density lipoproteins show different lipidomic pattern

In the present paper we have performed comparative lipidomic analysis of two prototypic atherogenic LDL modifications, oxidized LDL and enzymatically modified LDL. Oxidization of LDL was carried out with different chemical modifications starting from the same native LDL preparations: (i) by copper oxidation leading to terminally oxidized LDL (oxLDL), (ii) by moderate oxidization with HOCl (HOCl LDL), (iii) by long term storage of LDL at 4°C to produce minimally modified LDL (mmLDL), or (iv) by 15-lipoxygenase, produced by a transfected fibroblast cell line (LipoxLDL). The enzymatic modification of LDL was performed by treatment of native LDL with trypsin and cholesteryl esterase (eLDL). Free cholesterol (FC) and cholesteryl esters (CE) represent the predominant lipid classes in all LDL preparations. In contrast to native LDL, which contains about two-thirds of total cholesterol as CE, enzymatic modification of LDL decreased the proportion of CE to about one-third. Free cholesterol and CE in oxLDL are reduced by their conversion to oxysterols. Oxidization of LDL preferentially influences the content of polyunsaturated phosphatidylcholine (PC) and polyunsaturated plasmalogen species, by reducing the total PC fraction in oxLDL. Concomitantly, a strong rise of the lysophosphatidylcholine (LPC) fraction can be found in oxLDL as compared to native LDL. This effect is less pronounced in eLDL. The mild oxidation of LDL with hypochlorite and/or lipoxygenase does not alter the content of the analyzed lipid classes and species in a significant manner. The lipidomic characterization of modified LDLs contributes to the better understanding their diverse cellular effects.

ABCG1 is required for pulmonary B-1 B cell and natural antibody homeostasis

Many metabolic diseases, including atherosclerosis, type 2 diabetes, pulmonary alveolar proteinosis, and obesity, have a chronic inflammatory component involving both innate and adaptive immunity. Mice lacking the ATP-binding cassette transporter G1 (ABCG1) develop chronic inflammation in the lungs, which is associated with the lipid accumulation (cholesterol, cholesterol ester, and phospholipid) and cholesterol crystal deposition that are characteristic of atherosclerotic lesions and pulmonary alveolar proteinosis. In this article, we demonstrate that specific lipids, likely oxidized phospholipids and/or sterols, elicit a lung-specific immune response in Abcg1(-/-) mice. Loss of ABCG1 results in increased levels of specific oxysterols, phosphatidylcholines, and oxidized phospholipids, including 1-palmitoyl-2-(5'-oxovaleroyl)-sn-glycero-3-phosphocholine, in the lungs. Further, we identify a niche-specific increase in natural Ab (NAb)-secreting B-1 B cells in response to this lipid accumulation that is paralleled by increased titers of IgM, IgA, and IgG against oxidation-specific epitopes, such as those on oxidized low-density lipoprotein and malondialdehyde-modified low-density lipoprotein. Finally, we identify a cytokine/chemokine signature that is reflective of increased B cell activation, Ab secretion, and homing. Collectively, these data demonstrate that the accumulation of lipids in Abcg1(-/-) mice induces the specific expansion and localization of B-1 B cells, which secrete NAbs that may help to protect against the development of atherosclerosis. Indeed, despite chronic lipid accumulation and inflammation, hyperlipidemic mice lacking ABCG1 develop smaller atherosclerotic lesions compared with controls. These data also suggest that Abcg1(-/-) mice may represent a new model in which to study the protective functions of B-1 B cells/NAbs and suggest novel targets for pharmacologic intervention and treatment of disease.

Epigenetic regulation of cholesterol homeostasis

Although best known as a risk factor for cardiovascular disease, cholesterol is a vital component of all mammalian cells. In addition to key structural roles, cholesterol is a vital biochemical precursor for numerous biologically important compounds including oxysterols and bile acids, as well as acting as an activator of critical morphogenic systems (e.g., the Hedgehog system). A variety of sophisticated regulatory mechanisms interact to coordinate the overall level of cholesterol in cells, tissues and the entire organism. Accumulating evidence indicates that in additional to the more “traditional” regulatory schemes, cholesterol homeostasis is also under the control of epigenetic mechanisms such as histone acetylation and DNA methylation. The available evidence supporting a role for these mechanisms in the control of cholesterol synthesis, elimination, transport and storage are the focus of this review.