Oxysterols in biological systems: sources, metabolism and pathophysiological relevance

Discovery of a novel regulator, 3β-sulfate-5-cholestenoic acid, of lipid metabolism and inflammation

Mitochondrial oxysterols, cholestenoic acid (CA), 25-hydroxycholesterol (25HC), and 27-hydroxycholesterol (27HC), are potent regulators involved in many important biological events. This study aimed to investigate the metabolic pathways of these oxysterols and their roles between hepatocytes and macrophages. LC-MS/MS analysis showed a novel regulatory molecule, 3β-sulfate-5-cholestenoic acid (3SCA), following the addition of CA in media culturing hepatocytes. Further study showed that 3SCA could also be derived from 27HC. In comparison, 25HC was converted to 25HC3S, which mostly remained in the cells and nuclei. The functional study showed that 3SCA significantly downregulated the expression of genes involved in lipid metabolism in hepatocytes and suppressed gene expression of proinflammatory cytokines induced by lipopolysaccharide in human macrophages. Based on the results, we conclude that 3SCA acts as a secretory regulator for the regulation of lipid metabolism and inflammatory responses in hepatocytes and macrophages. These findings shed light on understanding the unique metabolic pathways of these oxysterols and their possible roles in liver tissues.NEW & NOTEWORTHY This study identifies a novel oxysterol metabolite, 3β-sulfate-5-cholestenoic acid (3SCA), secreted by hepatocytes, which regulates lipid metabolism and inflammatory responses in hepatocytes and macrophages. These findings reveal previously unknown metabolic pathways of mitochondrial oxysterols and their roles in the progression and recovery of metabolic dysfunction-associated steatotic liver disease (MASLD), offering novel insights into potential therapeutic targets.

Oxysterol sulfates in fluids, cells and tissues: how much do we know about their clinical significance, biological relevance and biophysical implications?

Oxysterol sulfates are emerging as key players in lipid homeostasis, inflammation and immunity. Despite this, knowledge on their basal levels in fluids, cells and tissues and any changes associated with age, gender and diet in health and disease; as well as their spatio-temporal distribution in cell membranes and organelles have been greatly hampered by the lack of commercially available pure synthetic standards. Expansion of the panel of pure oxysterol sulfates standards is pivotal to improve our understanding on the impact of oxysterol sulfates at the membrane level and their role in cellular events. While the clinical significance, biophysical implications and biological relevance of oxysterol sulfates in fluids, cells and tissues remains largely unknown, knowledge already gathered on the precursors of oxysterol sulfates (e.g. oxysterols and cholesterol sulfate) can be used to guide researchers on the most relevant aspects to search for when screening for oxysterol sulfates bioavailability in (patho)physiological conditions which are crucial in the design of biophysical and of cell-based assays. Herein, we provide a review on the brief knowledge involving oxysterol sulfate and an overview on the biophysical implications and biological relevance of oxysterols and cholesterol sulfate useful to redirect further investigations on the role of oxysterol sulfates in health and disease.

A Novel Method for the Determination of Squalene, Cholesterol and Their Oxidation Products in Food of Animal Origin by GC-TOF/MS

Cholesterol present in food of animal origin is a precursor of oxysterols (COPs), whose high intake through diet can be associated with health implications. Evaluation of the content of these contaminants in food is associated with many analytical problems. This work presents a GC-TOF/MS method for the simultaneous determination of squalene, cholesterol and seven COPs (7-ketocholesterol, 7α-hydroxycholesterol, 7β-hydroxycholesterol, 25-hydroxycholesterol, 5,6α-epoxycholesterol, 5,6β-epoxycholesterol, cholestanetriol). The sample preparation procedure includes such steps as saponification, extraction and silylation. The method is characterized by high sensitivity (limit of quantification, 0.02-0.25 ng mL-1 for instrument, 30-375 μg kg of sample), repeatability (RSD 2.3-6.2%) and a wide linearity range for each tested compound. The method has been tested on eight different animal-origin products. The COP to cholesterol content ratio in most products is about 1%, but the profile of cholesterol derivatives differs widely (α = 0.01). In all the samples, 7-ketocholesterol is the dominant oxysterol, accounting for 31-67% of the total COPs level. The levels of the other COPs range between 0% and 21%. In none of the examined products are cholestanetriol and 25-hydroxycholesterol present. The amount of squalene, which potentially may inhibit the formation of COPs in food, ranges from 2 to 57 mg kg-1.

Unraveling the versatility of human serum albumin - A comprehensive review of its biological significance and therapeutic potential

Human serum albumin (HSA) is a multi-domain macromolecule with diverse ligand binding capability because of its ability to allow allosteric modulation despite being a monomeric protein. Physiologically, HSA act as the primary carrier for various exogenous and endogenous compounds and fatty acids, and alter the pharmacokinetic properties of several drugs. It has antioxidant properties and is utilized therapeutically to improve the drug delivery of pharmacological agents for the treatment of several disorders. The flexibility of albumin in holding various types of drugs coupled with a variety of modifications makes this protein a versatile drug carrier with incalculable potential in therapeutics. This review provides a brief outline of the different structural properties of HSA, and its various binding sites, moreover, an overview of the genetic, biomedical, and allosteric modulation of drugs and drug delivery aspects of HSA is also included, which may be helpful in guiding advanced clinical applications and further research on the therapeutic potential of this extraordinary protein.

Cholesterol in colorectal cancer: an essential but tumorigenic precursor?

Colorectal cancer (CRC) is one of the most lethal human malignancies, and with the growth of societies and lifestyle changes, the rate of people suffering from it increases yearly. Important factors such as genetics, family history, nutrition, lifestyle, smoking, and alcohol can play a significant role in increasing susceptibility to this cancer. On the other hand, the metabolism of several macromolecules is also involved in the fate of tumors and immune cells. The evidence discloses that cholesterol and its metabolism can play a role in the pathogenesis of several cancers because there appears to be an association between cholesterol levels and CRC, and cholesterol-lowering drugs may reduce the risk. Furthermore, changes or mutations of some involved genes in cholesterol metabolism, such as CYP7A1 as well as signaling pathways, such as mitogen-activated protein kinase (MAPK), can play a role in CRC pathogenesis. This review summarized and discussed the role of cholesterol in the pathogenesis of CRC as well as available cholesterol-related therapeutic approaches in CRC.

A new modality for cholesterol impact tracking in colon cancer development - Raman imaging, fluorescence and AFM studies combined with chemometric analysis

Colorectal cancer (CRC) is the third most common cancer worldwide. Obesity, alcohol consumption, smoking, high consumption of red or processed meat and a diet with low fibre, fruit, and vegetable intake increase CRC risk. Despite advances in surgery (the basic treatment for recovery), chemotherapy, and radiotherapy, CRC remains the second leading cause of cancer-related deaths in the world. Therefore the social importance of this problem stimulates research aimed at developing new tools for rapid CRC diagnosis and analysis of CRC risk factors. Considering the association between the cholesterol level and CRC, we hypothesize that cholesterol spectroscopic and AFM (atomic force microscopy) studies combined with chemometric analysis can be new, powerful tools used to visualize the cholesterol distribution, estimate cholesterol content and determine its influence on the biochemical and nanomechanical properties of colon cells. Our paper presents the analysis of human colon tissues: normal and cancer and human colon single cells normal CCD18-Co and cancer CaCo-2 in the physiological state and CaCo-2 upon mevastatin supplementation. Based on vibrational features we have shown that Raman spectroscopy and imaging allow cholesterol content in human colon tissues and human colon single cells of both types to be tracked and allow the effectiveness of mevastatin in the mevalonate pathway modulation and disruption of the cholesterol level to be proven. All observations have been confirmed by chemometric analysis including principal component analysis (PCA) and partial least squares discriminant analysis (PLSDA). The positive impact of statins on cholesterol content has also been studied by using fluorescence microscopy and atomic force microscopy (AFM). A significant increase in Young modulus as a mechanomarker for CaCo-2 human cancer colon cells upon mevastatin supplementation compared to CCD18-Co human normal colon cells was observed. This paper is one of the first reports about the use of Raman spectroscopic techniques in cholesterol investigations and the first one about cholesterol investigation using Raman spectroscopy (RS) on human cells ex vivo in the context of colon cancer development.

Functional significance of cholesterol metabolism in cancer: from threat to treatment

Cholesterol is an essential structural component of membranes that contributes to membrane integrity and fluidity. Cholesterol homeostasis plays a critical role in the maintenance of cellular activities. Recently, increasing evidence has indicated that cholesterol is a major determinant by modulating cell signaling events governing the hallmarks of cancer. Numerous studies have shown the functional significance of cholesterol metabolism in tumorigenesis, cancer progression and metastasis through its regulatory effects on the immune response, ferroptosis, autophagy, cell stemness, and the DNA damage response. Here, we summarize recent literature describing cholesterol metabolism in cancer cells, including the cholesterol metabolism pathways and the mutual regulatory mechanisms involved in cancer progression and cholesterol metabolism. We also discuss various drugs targeting cholesterol metabolism to suggest new strategies for cancer treatment.

The role of cholesterol metabolism in tumor therapy, from bench to bed

Cholesterol and its metabolites have important biological functions. Cholesterol is able to maintain the physical properties of cell membrane, play an important role in cellular signaling, and cellular cholesterol levels reflect the dynamic balance between biosynthesis, uptake, efflux and esterification. Cholesterol metabolism participates in bile acid production and steroid hormone biosynthesis. Increasing evidence suggests a strict link between cholesterol homeostasis and tumors. Cholesterol metabolism in tumor cells is reprogrammed to differ significantly from normal cells, and disturbances of cholesterol balance also induce tumorigenesis and progression. Preclinical and clinical studies have shown that controlling cholesterol metabolism suppresses tumor growth, suggesting that targeting cholesterol metabolism may provide new possibilities for tumor therapy. In this review, we summarized the metabolic pathways of cholesterol in normal and tumor cells and reviewed the pre-clinical and clinical progression of novel tumor therapeutic strategy with the drugs targeting different stages of cholesterol metabolism from bench to bedside.

GC-MS analysis of oxysterols and their formation in cultivated liver cells (HepG2)

Oxysterols play a key role in many (patho)physiological processes and they are potential biomarkers for oxidative stress in several diseases. Here we developed a rapid gas chromatographic-mass spectrometry-based method for the separation and quantification of 11 biologically relevant oxysterols bearing hydroxy, epoxy, and dihydroxy groups. Efficient chromatographic separation (resolution ≥ 1.9) was achieved using a medium polarity 35%-diphenyl/65%-dimethyl polysiloxane stationary phase material (30 m × 0.25 mm inner diameter and 0.25 μm film thickness). Based on thorough analysis of the fragmentation during electron ionization we developed a strategy to deduce structural information of the oxysterols. Optimized sample preparation includes (i) extraction with a mixture of n-hexane/iso-propanol, (ii) removal of cholesterol by solid phase extraction with unmodified silica, and (iii) trimethylsilylation. The method was successfully applied on the analysis of brain samples, showing consistent results with previous studies and a good intra- and interday precision of ≤20%. Finally, we used the method for the investigation of oxysterol formation during oxidative stress in HepG2 cells. Incubation with tert-butyl hydroperoxide led to a massive increase in free radical formed oxysterols (7-keto-chol > 7β-OH-chol >> 7α-OH-chol), while 24 h incubation with the glutathione peroxidase 4 inhibitor RSL3 showed no increase in oxidative stress based on the oxysterol pattern. Overall, the new method described here enables the robust analysis of a biologically meaningful pattern of oxysterols with high sensitivity and precision allowing us to gain new insights in the biological formation and role of oxysterols.

Niemann-Pick type C disease as proof-of-concept for intelligent biomarker panel selection in neurometabolic disorders

AIM

Using Niemann-Pick type C disease (NPC) as a paradigm, we aimed to improve biomarker discovery in patients with neurometabolic disorders.

METHOD

Using a multiplexed liquid chromatography tandem mass spectrometry dried bloodspot assay, we developed a selective intelligent biomarker panel to monitor known biomarkers N-palmitoyl-O-phosphocholineserine and 3β,5α,6β-trihydroxy-cholanoyl-glycine as well as compounds predicted to be affected in NPC pathology. We applied this panel to a clinically relevant paediatric patient cohort (n = 75; 35 males, 40 females; mean age 7 years 6 months, range 4 days-19 years 8 months) presenting with neurodevelopmental and/or neurodegenerative pathology, similar to that observed in NPC.

RESULTS

The panel had a far superior performance compared with individual biomarkers. Namely, NPC-related established biomarkers used individually had 91% to 97% specificity but the combined panel had 100% specificity. Moreover, multivariate analysis revealed long-chain isoforms of glucosylceramide were elevated and very specific for patients with NPC.

INTERPRETATION

Despite advancements in next-generation sequencing and precision medicine, neurological non-enzymatic disorders remain difficult to diagnose and lack robust biomarkers or routine functional testing for genetic variants of unknown significance. Biomarker panels may have better diagnostic accuracy than individual biomarkers in neurometabolic disorders, hence they can facilitate more prompt disease identification and implementation of emerging targeted, disease-specific therapies.

WHAT THIS PAPER ADDS

Intelligent biomarker panel design can help expedite diagnosis in neurometabolic disorders. In Niemann-Pick type C disease, such a panel performed better than individual biomarkers. Biomarker panels are easy to implement and widely applicable to neurometabolic conditions.

Germline and somatic genetic variability of oxysterol-related genes in breast cancer patients with early disease of the luminal subtype

Oxysterols, oxidized derivatives of cholesterol, have been implicated in multiple pathologies, including cancer. In breast cancer, the link is especially strong due to interactions between oxysterols and estrogen receptor activity. Here, we provide the first dedicated study of 113 oxysterol-related genes in breast cancer patients of the luminal subtype, in terms of both their somatic and germline variability, using targeted high-throughput DNA sequencing of 100 normal-tumor pairs with very high coverage. In the full cohort, or subsets of patients stratified by therapy, we found 12 germline variants in ABCA1, ABCA8, ABCC1, GPR183, LDLR, MBTPS1, NR1I2, OSBPL2, OSBPL3, and OSBPL5 to associate with poor survival of patients and variants in ABCA8, ABCG2, and HSD3B7 (three in total) associated with better survival. However, no associations remained significant after correction for multiple tests. Analysis of somatic variants revealed significantly (after FDR correction) poorer survival in patients mutated in CYP46A1 and 9 interacting (according to STRING analysis) genes, as well as in OSBPL3 and a set of 20 genes that collectively associated with the progesterone receptor status of patients. We propose further exploration of these genes in an integrative manner together with gene expression and epigenomic data.

Aberrant Cholesterol Metabolism in Ovarian Cancer: Identification of Novel Therapeutic Targets

Cholesterol is an essential substance in mammalian cells, and cholesterol metabolism plays crucial roles in multiple biological functions. Dysregulated cholesterol metabolism is a metabolic hallmark in several cancers, beyond the Warburg effect. Reprogrammed cholesterol metabolism has been reported to enhance tumorigenesis, metastasis and chemoresistance in multiple cancer types, including ovarian cancer. Ovarian cancer is one of the most aggressive malignancies worldwide. Alterations in metabolic pathways are characteristic features of ovarian cancer; however, the specific role of cholesterol metabolism remains to be established. In this report, we provide an overview of the key proteins involved in cholesterol metabolism in ovarian cancer, including the rate-limiting enzymes in cholesterol biosynthesis, and the proteins involved in cholesterol uptake, storage and trafficking. Also, we review the roles of cholesterol and its derivatives in ovarian cancer and the tumor microenvironment, and discuss promising related therapeutic targets for ovarian cancer.

Serum Albumin: A Multifaced Enzyme

Human serum albumin (HSA) is the most abundant protein in plasma, contributing actively to oncotic pressure maintenance and fluid distribution between body compartments. HSA acts as the main carrier of fatty acids, recognizes metal ions, affects pharmacokinetics of many drugs, provides the metabolic modification of some ligands, renders potential toxins harmless, accounts for most of the anti-oxidant capacity of human plasma, and displays esterase, enolase, glucuronidase, and peroxidase (pseudo)-enzymatic activities. HSA-based catalysis is physiologically relevant, affecting the metabolism of endogenous and exogenous compounds including proteins, lipids, cholesterol, reactive oxygen species (ROS), and drugs. Catalytic properties of HSA are modulated by allosteric effectors, competitive inhibitors, chemical modifications, pathological conditions, and aging. HSA displays anti-oxidant properties and is critical for plasma detoxification from toxic agents and for pro-drugs activation. The enzymatic properties of HSA can be also exploited by chemical industries as a scaffold to produce libraries of catalysts with improved proficiency and stereoselectivity for water decontamination from poisonous agents and environmental contaminants, in the so called “green chemistry” field. Here, an overview of the intrinsic and metal dependent (pseudo-)enzymatic properties of HSA is reported to highlight the roles played by this multifaced protein.

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.

An advanced method for quantitative measurements of cholesterol crystallization

BACKGROUND

Cholesterol crystallization within an atherosclerotic plaque significantly contributes to the acceleration of plaque rupture - a problematic event due to the current lack of specific treatments to prevent such formations. Modelling this pathogenic process is also difficult due to the lack of suitable experimental models that enable quantitative analysis of crystal formation and bioactivity screening of potential therapeutic compounds.

AIM

To develop an in vitro human cell model of cholesterol crystallization combined with an imaging system that incorporates both quantitative analysis and real-time continuous imaging of cholesterol crystal formation.

METHODS AND RESULTS

An enhanced in vitro model of cholesterol crystallization was developed through the use of acetylated low-density lipoprotein (AcLDL) and 7-ketocholesterol as agents of foam cell induction within a human THP-1 monocytic cell line. Advanced confocal and polarizing microscopies were incorporated into the model so as to allow for quantitation of cholesterol crystallization, with the lipid-loaded group producing significantly greater numbers of cholesterol crystals than the untreated group. The utility of this system was also demonstrated by investigating the effects of the cholesterol-lowering drug lovastatin and therapeutic bile compound ursodeoxycholic acid (UDCA), showing that these drugs influence different aspects of cholesterol crystal formation.

CONCLUSIONS

The in vitro human THP-1 monocyte model of cholesterol crystallization provides an effective and efficient means of quantitating cholesterol crystallization in the pre-clinical stage of research. The model also allows for the screening of potentially therapeutic compounds that may be used in attenuating or preventing cholesterol crystallization.

Cholesterol metabolism: New functions and therapeutic approaches in cancer

Cholesterol and its metabolites (precursors and derivatives) play an important role in cancer. In recent years, numerous studies have reported the functions of cholesterol metabolism in the regulation of tumor biological processes, especially oncogenic signaling pathways, ferroptosis, and tumor microenvironment. Preclinical studies have over the years indicated the inhibitory effects of blocking cholesterol synthesis and uptake on tumor formation and growth. Besides, some new cholesterol metabolic molecules such as SOAT1, SQLE, and NPC1 have recently emerged as promising drug targets for cancer treatment. Here, we systematically review the roles of cholesterol and its metabolites, and the latest advances in cancer therapy targeting cholesterol metabolism.

Prednisolone suppresses the immunostimulatory effects of 27-hydroxycholesterol

In cholesterol-fed rabbits, site-specific targeting of prednisolone nanoparticles results in significantly reduced neo-intimal inflammation with a decreased infiltration of monocytes/macrophages. To understand the molecular mechanisms underlying this, the current study investigated whether prednisolone affects the immune attributes of 27-hydroxycholesterol (27OHChol), the major oxidized cholesterol molecule in circulation and tissue, in human (THP-1) monocyte/macrophage cells. THP-1 cells were exposed to 27OHChol in the presence of prednisolone followed by evaluation of inflammatory molecules at mRNA and protein levels by quantitative PCR, western blotting, ELISA and flow cytometry. The results revealed that prednisolone suppressed the 27OHChol-mediated expression of various macrophage (M)1 markers, including chemokine ligand 2, C-X-C chemokine motif 10, tumor necrosis factor-α and CD80. Treatment also impaired the 27OHCHol-enhanced migration of monocytic cells, downregulated the 27OHChol-induced cell surface expression of CD14 and inhibited the release of soluble CD14 comparable with a weakened lipopolysaccharide response. Furthermore, prednisolone suppressed the 27OHChol-induced expression of matrix metalloproteinase 9 at the transcriptional and protein level, as well as the phosphorylation of the p65 subunit. Prednisolone increased the transcription of CD163 and CD206 genes, and augmented the 27OHChol-induced transcription of CD163 without upregulating the 27OHChol-induced surface protein level of the gene. The results indicated that prednisolone inhibited the polarization of monocytes/macrophages towards the M1 phenotype, which that the immunostimulatory effects of 27OHCHol were being regulated and the immune responses in conditions that were rich in oxygenated cholesterol molecules were being modulated.

25-Hydroxycholesterol Inhibits Adipogenic Differentiation of C3H10T1/2 Pluripotent Stromal Cells

Understanding of adipogenesis is important to find remedies for obesity and related disorders. In addition, it is also critical in bone disorders because there is a reciprocal relationship between adipogenesis and osteogenesis in bone micro-environment. Oxysterols are pro-osteogenic and anti-adipogenic molecules via hedgehog activation in pluripotent bone marrow stomal cells. However, no study has evaluated the role of specific oxysterols in C3H10T1/2 cells, which are a good cell model for studying osteogenesis and adipogenesis in bone-marrows. Thus, we investigated the effects of specific oxysterols on adipogenesis and expression of adipogenic transcripts in C3H10T1/2 cells. Treatment of cells with DMITro significantly induced mRNA expression of Pparγ. This induction was significantly inhibited by 25-HC. The expression of C/cepα, Fabp4 and Lpl was also inhibited by 25-HC. To determine the mechanism by which 25-HC inhibits adipogenesis, the effects of the hedgehog signalling pathway inhibitor, cyclopamine and CUR61414, were evaluated. Treatment of C3H10T1/2 cells with DMITro + cyclopamine or DMITro + CUR61414 for 96h did not modulate adipocyte differentiation; cyclopamine and CUR61414 did not reverse the inhibitory effects of 25-HC, suggesting that the canonical hedgehog signalling may not play a role in the anti-adipogenic effects of 25-HC in C3H10T1/2 cells. In addition, LXR agonist did not inhibit adipogenesis, but 25-HC strongly inhibits adipogenesis of C3H10T1/2 cells. Our observations showed that 25-HC was the most potent oxysterol in inhibiting adipogenesis and the expression of key adipogenic transcripts in C3H10T1/2 cells among the tested oxysterols, suggesting its potential application in providing an intervention in osteoporosis and obesity. We also report that the inhibitory effects of 25-HC on adipogenic differentiation in C3H10T1/2 cells are not mediated by hedgehog signaling and LXR.

Even Cancer Cells Watch Their Cholesterol!

Deregulated cell proliferation is an established feature of cancer, and altered tumor metabolism has witnessed renewed interest over the past decade, including the study of how cancer cells rewire metabolic pathways to renew energy sources and "building blocks" that sustain cell division. Microenvironmental oxygen, glucose, and glutamine are regarded as principal nutrients fueling tumor growth. However, hostile tumor microenvironments render O₂/nutrient supplies chronically insufficient for increased proliferation rates, forcing cancer cells to develop strategies for opportunistic modes of nutrient acquisition. Recent work shows that cancer cells overcome this nutrient scarcity by scavenging other substrates, such as proteins and lipids, or utilizing adaptive metabolic pathways. As such, reprogramming lipid metabolism plays important roles in providing energy, macromolecules for membrane synthesis, and lipid-mediated signaling during cancer progression. In this review, we highlight more recently appreciated roles for lipids, particularly cholesterol and its derivatives, in cancer cell metabolism within intrinsically harsh tumor microenvironments.

Localisation of oxysterols at the sub-cellular level and in biological fluids

Oxysterols are oxidized derivatives of cholesterol that are formed enzymatically or via reactive oxygen species or both. Cholesterol or oxysterols ingested as food are absorbed and packed into lipoproteins that are taken up by hepatic cells. Within hepatic cells, excess cholesterol is metabolised to form bile acids. The endoplasmic reticulum acts as the main organelle in the bile acid synthesis pathway. Metabolised sterols originating from this pathway are distributed within other organelles and in the cell membrane. The alterations to membrane oxysterol:sterol ratio affects the integrity of the cell membrane. The presence of oxysterols changes membrane fluidity and receptor orientation. It is well documented that hydroxylase enzymes located in mitochondria facilitate oxysterol production via an acidic pathway. More recently, the presence of oxysterols was also reported in lysosomes. Peroxisomal deficiencies favour intracellular oxysterols accumulation. Despite the low abundance of oxysterols compared to cholesterol, the biological actions of oxysterols are numerous and important. Oxysterol levels are implicated in the pathogenesis of multiple diseases ranging from chronic inflammatory diseases (atherosclerosis, Alzheimer's disease and bowel disease), cancer and numerous neurodegenerative diseases. In this article, we review the distribution of oxysterols in sub-cellular organelles and in biological fluids.

Cholesterol Degradation and Production of Extracellular Cholesterol Oxidase from Bacillus pumilus W1 and Serratia marcescens W8

Cholesterol is a waxy substance present in all types of the body cells. The presence of higher concentration of low density lipoprotein (LDL) is characterized by abnormal cholesterol level and is associated with cardiovascular diseases which lead to the development of atheroma in arteries known as atherosclerosis. The transformation of cholesterol by bacterial cholesterol oxidase can provide a key solution for the treatment of diseases related to cholesterol and its oxidized derivatives. Previously isolated bacteria from oil-contaminated soil were screened for cholesterol degradation. Among fourteen, five isolates were able to utilize cholesterol. Two strains Serratia marcescens W1 and Bacillus pumilus W8 using cholesterol as only carbon and energy source were selected for degradation studies. Several parameters (incubation time, substrate concentration, pH, temperature, and different metal ions) for cholesterol decomposition by the selected bacterial strains were evaluated. Maximum cholesterol reduction was achieved on the 5th day of incubation, 1g/L of substrate concentration, pH 7, in the presence of Mg2+ and Ca2+ ions, and at 35°C. Cholesterol degradation was analyzed by enzymatic colorimetric method, thin layer chromatography (TLC), and high-performance liquid chromatography (HPLC). Under optimized conditions 50% and 84% cholesterol reduction were recorded with Serratia marcescens W1 and Bacillus pumilus W8, respectively. Cholesterol oxidase activity was assayed qualitatively and quantitatively. The results revealed that Serratia marcescens W1 and Bacillus pumilus W8 have great potential for cholesterol degradation and would be regarded as a source for cholesterol oxidase (CHO).

7-Ketocholesterol enhances leukocyte adhesion to endothelial cells via p38MAPK pathway

7-Ketocholesterol is a major dietary cholesterol oxidation product found in high concentrations in atherosclerotic plaques, which contribute to the development of atherosclerosis. This study aimed to investigate the effects of 7-ketocholesterol on endothelial inflammation, as well as the underlying mechanisms. Pretreatment of human umbilical vein endothelial cells (HUVEC) with 7-ketocholesterol significantly enhanced the total interactions between human monocytic cells (THP-1 cell line) and TNFα-activated HUVECs under physiological flow conditions, compared to pretreatment with cholesterol (TNFα+50 μM cholesterol: 13.1 ± 0.54 cells/CPF, TNFα+50 μM 7-ketocholesterol: 18.9 ± 0.35 cells/CPF, p < 0.01). 7-Ketocholesterol enhanced the expression of E-selectin, ICAM-1, and VCAM-1 proteins. It also activated p38 mitogen-activated protein kinase (MAPK), and treatment with a p38 MAPK inhibitor inhibited both E-selectin expression via ATF-2 activation and 7-ketocholesterol-induced THP-1 adhesion to HUVECs. These findings suggest that 7-ketocholesterol enhances leukocyte–endothelial interactions by upregulating the expression of adhesion molecules, presumably via the p38 MAPK-dependent pathway.

7-Ketocholesterol induces ROS-mediated mRNA expression of 12-lipoxygenase, cyclooxygenase-2 and pro-inflammatory cytokines in human mesangial cells: Potential role in diabetic nephropathy

7-Ketocholesterol (7-KCHO) is a highly proinflammatory oxysterol and plays an important role in the pathophysiology of diabetic nephropathy (DN). Lipoxygenases (LOXs) and cyclooxygenases (COXs) are also involved in the development of DN. The aim of this study was to clarify the effects of 7-KCHO on mRNA expression of LOXs and COXs as well as pro-inflammatory cytokines in human mesangial cells (HMC). We evaluated cell viability by WST-8 assay and measured mRNA expression by reverse transcription-polymerase chain reaction. Intracellular reactive oxygen species (ROS) production was evaluated by flow cytometry. Although 7-KCHO did not affect cell viability of HMC, 7-KCHO stimulated significant increases in mRNA expression of 12-LOX, COX-2 and pro-inflammatory cytokines. 7-KCHO also induced an increase in ROS production, while N-acetylcysteine partially suppressed the increase. The 12-LOX and COX-2 inhibitors also suppressed mRNA expression of cytokines. These findings may contribute to the elucidation of the molecular mechanism of the pathophysiology of DN.

The balance between induction and inhibition of mevalonate pathway regulates cancer suppression by statins: A review of molecular mechanisms

Statins are widely used drugs for their role in decreasing cholesterol in hypercholesterolemic patients. Statins through inhibition of Hydroxy Methyl Glutaryl-CoA Reductase (HMGCR), the main enzyme of the cholesterol biosynthesis pathway, inhibit mevalonate pathway that provides isoprenoids for prenylation of different proteins such as Ras superfamily which has an essential role in cancer developing. Inhibition of the mevalonate/isoprenoid pathway is the cause of the cholesterol independent effects of statins or pleotropic effects. Depending on their penetrance into the extra-hepatic cells, statins have different effects on mevalonate/isoprenoid pathway. Lipophilic statins diffuse into all cells and hydrophilic ones use a variety of membrane transporters to gain access to cells other than hepatocytes. It has been suggested that the lower accessibility of statins for extra-hepatic tissues may result in the compensatory induction of mevalonate/isoprenoid pathway and so cancer developing. However, most of the population-based studies have demonstrated that statins have no effect on cancer developing, even decrease the risk of different types of cancer. In this review we focus on the cancer developing "potentials" and the anti-cancer "activities" of statins regarding the effects of statins on mevalonate/isoprenoid pathway in the liver and extra-hepatic tissues.

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.

Plant sterols, cholesterol precursors and oxysterols: Minute concentrations-Major physiological effects

Non-cholesterol sterols are present in our body at very low concentrations as compared to cholesterol. Small changes in the structure of sterol molecules confer them highly distinct biological activities. The best-known example are steroid hormones derived from cholesterol. During the past decade, our knowledge of also other biomolecules related to or derived from cholesterol, particularly plant sterols, biosynthetic precursors of cholesterol, and oxysterols, has expanded rapidly. In this review article we recapitulate the latest insights into the properties and physiological activities of these non-cholesterol sterols, as well as their importance in disease processes and potential as diagnostic biomarkers.

7-ketocholesterol induces apoptosis of MC3T3-E1 cells associated with reactive oxygen species generation, endoplasmic reticulum stress and caspase-3/7 dependent pathway

Type 2 diabetes mellitus (T2DM) is associated with an increased risk of bone fractures without reduction of bone mineral density. The cholesterol oxide 7-ketocholesterol (7KCHO) has been implicated in numerous diseases such as atherosclerosis, Alzheimer's disease, Parkinson's disease, cancer, age-related macular degeneration and T2DM. In the present study, 7KCHO decreased the viability of MC3T3-E1 cells, increased reactive oxygen species (ROS) production and apoptotic rate, and upregulated the caspase-3/7 pathway. Furthermore, these effects of 7KCHO were abolished by pre-incubation of the cells with N-acetylcysteine (NAC), an ROS inhibitor. Also, 7KCHO enhanced the mRNA expression of two endoplasmic reticulum (ER) stress markers; CHOP and GRP78, in MC3T3-E1 cells. Pre-incubation of the cells with NAC suppressed the 7KCHO-induced upregulation of CHOP, but not GRP78. In conclusion, we demonstrated that 7KCHO induced apoptosis of MC3T3-E1 cells associated with ROS generation, ER stress, and caspase-3/7 activity, and the effects of 7KCHO were abolished by the ROS inhibitor NAC. These findings may provide new insight into the relationship between oxysterol and pathophysiology of osteoporosis seen in T2DM.

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We examined the effects of 7-ketocholesterol (7KCHO) on MC3T3-E1 cells.

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7KCHO increased reactive oxygen species (ROS) and apoptosis.

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7KCHO enhanced CHOP and GRP78 expression.

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N-acetylcysteine suppressed 7KCHO-induced ROS, apoptosis and CHOP expression.

Lipids, oxidized lipids, oxidation-specific epitopes, and Age-related Macular Degeneration

Age-related Macular Degeneration (AMD) is the leading cause of blindness among the elderly in western societies. While antioxidant micronutrient treatment is available for intermediate non-neovascular disease, and effective anti-vascular endothelial growth factor treatment is available for neovascular disease, treatment for early AMD is lacking due to an incomplete understanding of the early molecular events. The role of lipids, which accumulate in the macula, and their oxidation, has emerged as an important factor in disease development. These oxidized lipids can either directly contribute to tissue injury or react with amine on proteins to form oxidation-specific epitopes, which can induce an innate immune response. If inadequately neutralized, the inflammatory response from these epitopes can incite tissue injury during disease development. This review explores how the accumulation of lipids, their oxidation, and the ensuing inflammatory response might contribute to the pathogenesis of AMD. This article is part of a Special Issue entitled: Lipid modification and lipid peroxidation products in innate immunity and inflammation edited by Christoph J. Binder .

Oxidized LDL at the crossroads of immunity in non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is viewed as the hepatic manifestation of the metabolic syndrome and is a condition hallmarked by lipid accumulation in the liver (steatosis) along with inflammation (hepatitis). Currently, the etiology and mechanisms leading to obesity-induced hepatic inflammation are not clear and, as a consequence, strategies to diagnose or treat NASH in an accurate manner do not exist. In the current review, we put forward the concept of oxidized lipids as a significant risk factor for NASH. We will focus on the contribution of the different types of oxidized lipids as part of the oxidized low-density lipoprotein (oxLDL) to the hepatic inflammatory response. Furthermore, we will elaborate on the underlying mechanisms linking oxLDL to inflammatory responses in the liver and on how these cascades can be used as therapeutic targets to combat NASH. This article is part of a Special Issue entitled: Lipid modification and lipid peroxidation products in innate immunity and inflammation edited by Christoph J. Binder.

Tumor cell survival pathways activated by photodynamic therapy: a molecular basis for pharmacological inhibition strategies

Photodynamic therapy (PDT) has emerged as a promising alternative to conventional cancer therapies such as surgery, chemotherapy, and radiotherapy. PDT comprises the administration of a photosensitizer, its accumulation in tumor tissue, and subsequent irradiation of the photosensitizer-loaded tumor, leading to the localized photoproduction of reactive oxygen species (ROS). The resulting oxidative damage ultimately culminates in tumor cell death, vascular shutdown, induction of an antitumor immune response, and the consequent destruction of the tumor. However, the ROS produced by PDT also triggers a stress response that, as part of a cell survival mechanism, helps cancer cells to cope with the PDT-induced oxidative stress and cell damage. These survival pathways are mediated by the transcription factors activator protein 1 (AP-1), nuclear factor E2-related factor 2 (NRF2), hypoxia-inducible factor 1 (HIF-1), nuclear factor κB (NF-κB), and those that mediate the proteotoxic stress response. The survival pathways are believed to render some types of cancer recalcitrant to PDT and alter the tumor microenvironment in favor of tumor survival. In this review, the molecular mechanisms are elucidated that occur post-PDT to mediate cancer cell survival, on the basis of which pharmacological interventions are proposed. Specifically, pharmaceutical inhibitors of the molecular regulators of each survival pathway are addressed. The ultimate aim is to facilitate the development of adjuvant intervention strategies to improve PDT efficacy in recalcitrant solid tumors.

Arterial tissue and plasma concentration of enzymatic-driven oxysterols are associated with severe peripheral atherosclerotic disease and systemic inflammatory activity

INTRODUCTION

Cholesterol undergoes oxidation via both enzymatic stress- and free radical-mediated mechanisms, generating a wide range of oxysterols. In contrast to oxidative stress-driven metabolites, enzymatic stress-derived oxysterols are scarcely studied in their association with atherosclerotic disease in humans.

METHODS

24S-hydroxycholesterol (24S-HC), 25-hydroxycholesterol (25-HC), and 27-hydroxycholesterol (27-HC) were assessed in plasma and arteries with atherosclerotic plaques from 10 patients (54-84 years) with severe peripheral artery disease (PAD) as well as arteries free of atherosclerotic plaques from 13 individuals (45-78 years, controls).

RESULTS

Plasma 25-HC was higher in PAD individuals than in controls (6.3[2] vs. 3.9[1.9] ng/mgCol; p = 0.004). 24S-HC and 27-HC levels were, respectively, five- and 20-fold higher in the arterial tissue of PAD individuals than in those of the controls (p = 0.016 and p = 0.001). Plasma C-reactive protein correlated with plasma 24-HC (r = 0.51; p = 0.010), 25-HC (r = 0.75; p < 0.001), 27-HC (r = 0.48; p = 0.015), and with tissue 24S-HC (r = 0.4; p = 0.041) and 27-HC (r = 0.46; p = 0.023).

CONCLUSION

Arterial intima accumulation of 27-HC and 24S-HC is associated with advanced atherosclerotic disease and systemic inflammatory activity in individuals with severe PAD.

Identification of novel regulatory cholesterol metabolite, 5-cholesten, 3β,25-diol, disulfate

Oxysterol sulfation plays an important role in regulation of lipid metabolism and inflammatory responses. In the present study, we report the discovery of a novel regulatory sulfated oxysterol in nuclei of primary rat hepatocytes after overexpression of the gene encoding mitochondrial cholesterol delivery protein (StarD1). Forty-eight hours after infection of the hepatocytes with recombinant StarD1 adenovirus, a water-soluble oxysterol product was isolated and purified by chemical extraction and reverse-phase HPLC. Tandem mass spectrometry analysis identified the oxysterol as 5-cholesten-3β, 25-diol, disulfate (25HCDS), and confirmed the structure by comparing with a chemically synthesized compound. Administration of 25HCDS to human THP-1-derived macrophages or HepG2 cells significantly inhibited cholesterol synthesis and markedly decreased lipid levels in vivo in NAFLD mouse models. RT-PCR showed that 25HCDS significantly decreased SREBP-1/2 activities by suppressing expression of their responding genes, including ACC, FAS, and HMG-CoA reductase. Analysis of lipid profiles in the liver tissues showed that administration of 25HCDS significantly decreased cholesterol, free fatty acids, and triglycerides by 30, 25, and 20%, respectively. The results suggest that 25HCDS inhibits lipid biosynthesis via blocking SREBP signaling. We conclude that 25HCDS is a potent regulator of lipid metabolism and propose its biosynthetic pathway.

7-Ketocholesterol-induced inflammation signals mostly through the TLR4 receptor both in vitro and in vivo

The cholesterol oxide 7-ketocholesterol (7KCh) has been implicated in numerous age-related diseases such as atherosclerosis, Alzheimer's disease, Parkinson's disease, cancer and age-related macular degeneration. It is formed by the autooxidation of cholesterol and especially cholesterol-fatty acid esters found in lipoprotein deposits. This molecule causes complex and potent inflammatory responses in vitro and in vivo. It is suspected of causing chronic inflammation in tissues exposed to oxidized lipoprotein deposits. In this study we have examined the inflammatory pathways activated by 7KCh both in cultured ARPE19 cells and in vivo using 7KCh-containing implants inserted into the anterior chamber of the rat eye. Our results indicate that 7KCh-induced inflammation is mediated mostly though the TLR4 receptor with some cross-activation of EGFR-related pathways. The majority of the cytokine inductions seem to signal via the TRIF/TRAM side of the TLR4 receptor. The MyD88/TIRAP side only significantly effects IL-1β inductions. The 7KCh-induced inflammation also seems to involve a robust ER stress response. However, this response does not seem to involve a calcium efflux-mediated UPR. Instead the ER stress response seems to be mediated by yet identified kinases activated through the TLR4 receptor. Some of the kinases identified are the RSKs which seem to mediate the cytokine inductions and the cell death pathway but do not seem to be involved in the ER stress response.

Increased serum oxysterol concentrations in patients with chronic hepatitis C virus infection

Oxidative stress and dysregulated cholesterol metabolism are characteristic features of chronic hepatitis C virus infection (CHC). Therefore, we analyzed serum oxysterol profiles in CHC patients and examined the significance of oxysterols in CHC. The concentrations of 7α-hydroxycholesterol, 4β-hydroxycholesterol and 25-hydroxycholesterol as determined by LC-ESI-MS/MS were significantly elevated by +236%, +29% and +44%, respectively, in CHC patients compared with controls. Moreover, the elevated levels were significantly decreased by anti-viral therapy using PEGylated-interferon and ribavirin for 3 months. In contrast, 24S-hydroxycholesterol, 27-hydroxycholesterol and 7α-hydroxy-4-cholesten-3-one concentrations were not affected by CHC or anti-viral treatment. These results suggest that some oxysterols that are elevated in CHC are produced by cholesterol autoxidation due to oxidative stress or inflammation in the liver. Oxysterols may represent novel targets for the inhibition of disease progression and the prevention of hepatocarcinogenesis in CHC patients.

Cholesterol hydroperoxides and their degradation mechanism

Cholesterol is one of the oxidizable lipids constituting biomembranes and plasma lipoproteins. Cholesterol hydroperoxides (Chol-OOH) are the primary products if cholesterol is subjected to attack by reactive oxygen species. In particular, singlet molecular oxygen reacts with cholesterol to yield cholesterol 5α-hydroperoxide as the major hydroperoxide species. Chol-OOH may accumulate in biological systems because of its resistance to glutathione-dependent enzymatic detoxification reactions. Their degradation products (including hydroxycholesterol and 7-ketocholesterol) participate in the pathophysiological functions of oxysterols. Highly reactive cholesterol 5,6-secosterol present in atherosclerotic lesions can be derived from the degradation of cholesterol 5α-hydroperoxide. Chol-OOH themselves may affect the lipid rafts of biomembranes, thereby leading to the modification of signal transduction pathways.

5-cholesten-3β,25-diol 3-sulfate decreases lipid accumulation in diet-induced nonalcoholic fatty liver disease mouse model

Sterol regulatory element-binding protein-1c (SREBP-1c) increases lipogenesis at the transcriptional level, and its expression is upregulated by liver X receptor α (LXRα). The LXRα/SREBP-1c signaling may play a crucial role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). We previously reported that a cholesterol metabolite, 5-cholesten-3β,25-diol 3-sulfate (25HC3S), inhibits the LXRα signaling and reduces lipogenesis by decreasing SREBP-1c expression in primary hepatocytes. The present study aims to investigate the effects of 25HC3S on lipid homeostasis in diet-induced NAFLD mouse models. NAFLD was induced by feeding a high-fat diet (HFD) in C57BL/6J mice. The effects of 25HC3S on lipid homeostasis, inflammatory responses, and insulin sensitivity were evaluated after acute treatments or long-term treatments. Acute treatments with 25HC3S decreased serum lipid levels, and long-term treatments decreased hepatic lipid accumulation in the NAFLD mice. Gene expression analysis showed that 25HC3S significantly suppressed the SREBP-1c signaling pathway that was associated with the suppression of the key enzymes involved in lipogenesis: fatty acid synthase, acetyl-CoA carboxylase 1, and glycerol-3-phosphate acyltransferase. In addition, 25HC3S significantly reduced HFD-induced hepatic inflammation as evidenced by decreasing tumor necrosis factor and interleukin 1 α/β mRNA levels. A glucose tolerance test and insulin tolerance test showed that 25HC3S administration improved HFD-induced insulin resistance. The present results indicate that 25HC3S as a potent endogenous regulator decreases lipogenesis, and oxysterol sulfation can be a key protective regulatory pathway against lipid accumulation and lipid-induced inflammation in vivo.

7-Ketocholesterol induces inflammation and angiogenesis in vivo: a novel rat model

Accumulation of 7-Ketocholesterol (7KCh) in lipid deposits has been implicated in a variety of chronic diseases including atherosclerosis, Alzheimer's disease and age-related macular degeneration. 7KCh is known to be pro-inflammatory and cytotoxic to various types of cultured cells but little is known about its effects in vivo. In this study we have investigated the effects of 7KCh in vivo by implanting biodegradable wafers into the anterior chamber of the rat eye. The wafers were prepared using a mixture of two biodegradable polymers with different amounts of 7KCh. The 7KCh-containing implants induced massive angiogenesis and inflammation. By contrast, no angiogenesis and very little inflammation were observed with cholesterol-containing implants. The neovessel growth was monitored by fluorescein angiography. Neovessels were observed 4 days post implantation and peaked between 7 to 10 days. The angiography and isolectin IB(4) labeling demonstrated that the neovessels originated from the limbus and grew through the cornea. Immunolabeling with anti-CD68 suggested that the 7KCh-containing implants had extensive macrophage infiltration as well as other cell types. A significant increase in VEGF was also observed in 7KCh-containing implants by fluorescent immunolabeling and by immunoblot of the aqueous humor (AH). Direct measurement of VEGF, IL-1β and GRO/KC demonstrated a marked elevation of these factors in the AH of the 7KCh-implants. In summary this study demonstrates two important things: 1) 7KCh is pro-angiogenic and pro-inflammatory in vivo and 2) implants containing 7KCh may be used to create a novel angiogenesis model in rats.

Regulation of the expression of interleukin-8 induced by 25-hydroxycholesterol in retinal pigment epithelium cells

PURPOSE

This study aimed at elucidating the molecular mechanisms involved in the regulation of IL-8 production by several oxysterols in retinal pigment epithelium (RPE) cells.

METHODS

A human cell line from RPE (ARPE-19) was used to test the role of cholesterol and several oxysterols (25-OH, 7-KC and 7β-OH) in the expression and secretion of IL-8. Expression of IL-8 was assessed by real-time PCR, while IL-8 secretion was evaluated by ELISA. PI3K-, MEK1/2-, ERK1/2- and NF-κB-specific inhibitors were used to assess the specific role of the several players on the regulation of IL-8 production by oxysterols. A gene-reporter assay for AP-1 activity was also conducted to evaluate the putative role of this transcription factor on IL-8 expression induced by oxysterols.

RESULTS

Here, we demonstrate that 25-OH specifically increases transcription and secretion of the cytokine IL-8 in ARPE-19 cells. Indeed, treatment of ARPE-19 with 25-OH, but not with 7-KC, 7β-OH or cholesterol, induced the secretion of IL-8 from cells. 25-OH also induced the activation/phosphorylation of ERK1/2 through a mechanism dependent on MEK, ERK1/2 and PI3K kinase activity. Real-time PCR and ELISA experiments demonstrated that 25-OH increased transcription and secretion of IL-8 through a mechanism that is dependent on ERK1/2 and PI3K activity. Furthermore, 25-OH triggered the activation/phosphorylation of the AP-1 component c-Jun and, consistently, increased the transcriptional activity of AP-1. Additionally, we also found that 25-OH decreases the levels of IκB and increases the nuclear levels of NF-κB p65 subunit and that inhibition of NF-κB activity partially prevents the increased secretion of IL-8 induced by 25-OH.

CONCLUSIONS

The results presented in this study suggest a role for 25-OH in inducing IL-8 production through pathways that are likely to involve AP-1 and NF-κB in ARPE-19 cells. Our data may also provide new molecular targets for the treatment of AMD.

Human serum albumin: from bench to bedside

Human serum albumin (HSA), the most abundant protein in plasma, is a monomeric multi-domain macromolecule, representing the main determinant of plasma oncotic pressure and the main modulator of fluid distribution between body compartments. HSA displays an extraordinary ligand binding capacity, providing a depot and carrier for many endogenous and exogenous compounds. Indeed, HSA represents the main carrier for fatty acids, affects pharmacokinetics of many drugs, provides the metabolic modification of some ligands, renders potential toxins harmless, accounts for most of the anti-oxidant capacity of human plasma, and displays (pseudo-)enzymatic properties. HSA is a valuable biomarker of many diseases, including cancer, rheumatoid arthritis, ischemia, post-menopausal obesity, severe acute graft-versus-host disease, and diseases that need monitoring of the glycemic control. Moreover, HSA is widely used clinically to treat several diseases, including hypovolemia, shock, burns, surgical blood loss, trauma, hemorrhage, cardiopulmonary bypass, acute respiratory distress syndrome, hemodialysis, acute liver failure, chronic liver disease, nutrition support, resuscitation, and hypoalbuminemia. Recently, biotechnological applications of HSA, including implantable biomaterials, surgical adhesives and sealants, biochromatography, ligand trapping, and fusion proteins, have been reported. Here, genetic, biochemical, biomedical, and biotechnological aspects of HSA are reviewed.

Enhanced production of 24S-hydroxycholesterol is not sufficient to drive liver X receptor target genes in vivo

BACKGROUND

Oxysterols such as 24S-hydroxycholesterol (OHC) and 27-OHC are intermediates of cholesterol excretion pathways. In addition, they are putative endogenous agonists of the liver X receptor (LXR) class of nuclear hormone receptors and are thought to be important mediators of cholesterol-dependent gene regulation. 24S-OHC is one of the most efficient endogenous LXR agonists known and is present in the brain and in the circulation at relatively high levels.

OBJECTIVES

To explore the regulatory importance of 24S-OHC in vivo.

DESIGN

We developed a transgenic mouse model in which human cholesterol 24-hydroxylase, the enzyme responsible for the formation of 24S-OHC, was expressed under the control of a promoter derived from the β-actin gene.

RESULTS

Both male and female transgenic mice had elevated levels of cerebral, plasma, biliary and faecal 24S-OHC. According to the faecal excretion results, production of 24S-OHC was increased four- to sevenfold. Gene expression profiling revealed that the elevated production of 24S-OHC did not result in the anticipated activation of LXR target genes in the brain or liver.

CONCLUSION

In spite of the fact that 24S-OHC is a highly effective agonist of LXRs in vitro, it is not a critical activator of target genes to this nuclear receptor in vivo, either in the brain or in the liver.

Short-term hyperglycemia increases arterial superoxide production and iron dysregulation in atherosclerotic monkeys

The incidence and severity of atherosclerotic vascular disease are increased in diabetic patients, in part because of increased production of reactive oxygen species (ROS). Previously, we found both increased atherosclerosis and arterial protein oxidation 6 months after streptozotocin-induced diabetes in monkeys fed an atherogenic diet, the pattern of which was indicative of redox-active transition metal involvement. The goal of this study was to determine if short-term (1 month) hyperglycemia increases oxidative stress and dysregulates iron metabolism before differences in atherosclerosis. Cynomolgus monkeys with preexisting atherosclerosis were stratified by dietary history and plasma lipids and received either streptozotocin (STZ-DM; n = 10) or vehicle (control; n = 10). One month after diabetes induction, blood and artery samples were collected. There were no differences in plasma lipoprotein cholesterol, arterial cholesterol, and atherosclerosis between control and STZ-DM. However, plasma lipid peroxides were elevated 137% (P < .01); arterial superoxide was increased 47% (P < .05); plasma ferritin, an indicator of whole-body iron stores, was 46% higher (P < .05); and iron deposition within aortic atherosclerotic lesions was more prevalent in STZ-DM compared with controls. Arterial levels of the antioxidant enzymes, superoxide dismutase, catalase, and heme oxygenase-1 were not higher in STZ-DM, although superoxide was higher, suggesting impaired antioxidant response. The increase in ROS before differences in atherosclerosis supports ROS as an initiating event in diabetic vascular disease. Further studies are needed to determine if increases in iron stores and arterial iron deposition promote hydroxyl radical formation from superoxide and accelerate diabetic vascular damage.

α-Tocopherol impairs 7-ketocholesterol-induced caspase-3-dependent apoptosis involving GSK-3 activation and Mcl-1 degradation on 158N murine oligodendrocytes

In important and severe neurodegenerative pathologies, 7-ketocholesterol, mainly resulting from cholesterol autoxidation, may contribute to dys- or demyelination processes. On various cell types, 7-ketocholesterol has often been shown to induce a complex mode of cell death by apoptosis associated with phospholipidosis. On 158N murine oligodendrocytes treated with 7-ketocholesterol (20 μg/mL corresponding to 50 μM, 24-48 h), the induction of a mode of cell death by apoptosis characterised by the occurrence of cells with condensed and/or fragmented nuclei, caspase activation (including caspase-3) and internucleosomal DNA fragmentation was observed. It was associated with a loss of transmembrane mitochondrial potential (ΔΨm) measured with JC-1, with a dephosphorylation of Akt and GSK3 (especially GSK3β), and with degradation of Mcl-1. With α-tocopherol (400 μM), which was capable of counteracting 7-ketocholesterol-induced apoptosis, Akt and GSK3β dephosphorylation were inhibited as well as Mcl-1 degradation. These data underline that the potential protective effects of α-tocopherol against 7-ketocholesterol-induced apoptosis do not depend on the cell line considered, and that the cascade of events (Akt/GSK3β/Mcl-1) constitutes a link between 7-ketocholesterol-induced cytoplasmic membrane dysfunctions and mitochondrial depolarisation leading to apoptosis.

Mechanisms of oxysterol-induced carcinogenesis

Oxysterols are oxidation products of cholesterol that are generated by enzymatic reactions mediated by cytochrome P450 family enzymes or by non-enzymatic reactions involving reactive oxygen and nitrogen species. Oxysterols play various regulatory roles in normal cellular processes such as cholesterol homeostasis by acting as intermediates in cholesterol catabolism. Pathological effects of oxysterols have also been described, and various reports have implicated oxysterols in several disease states, including atherosclerosis, neurological disease, and cancer. Numerous studies show that oxysterols are associated with various types of cancer, including cancers of the colon, lung, skin, breast and bile ducts. The molecular mechanisms whereby oxysterols contribute to the initiation and progression of cancer are an area of active investigation. This review focuses on the current state of knowledge regarding the role of oxysterols in carcinogenesis. Mutagenicity of oxysterols has been described in both nuclear and mitochondrial DNA. Certain oxysterols such as cholesterol-epoxide and cholestanetriol have been shown to be mutagenic and genotoxic. Oxysterols possess pro-oxidative and pro-inflammatory properties that can contribute to carcinogenesis. Oxysterols can induce the production of inflammatory cytokines such as interleukin-8 and interleukin-1β. Certain oxysterols are also involved in the induction of cyclo-oxygenase-2 expression. Inflammatory effects can also be mediated through the activation of liver-X-receptor, a nuclear receptor for oxysterols. Thus, several distinct molecular mechanisms have been described showing that oxysterols contribute to the initiation and progression of cancers arising in various organ systems.

Oxysterols: A world to explore

Oxysterols (oxidized derivatives of cholesterol and phytosterols) can be generated in the human organism through different oxidation processes, some requiring enzymes. Furthermore, oxysterols are also present in food due to lipid oxidation reactions caused by heating treatments, contact with oxygen, exposure to sunlight, etc., and they could be absorbed from the diet, at different rates depending on their side chain length. In the organism, oxysterols can follow different routes: secreted into the intestinal lumen, esterified and distributed by lipoproteins to different tissues or degraded, mainly in the liver. Cholesterol oxidation products (COPs) have shown cytotoxicity, apoptotic and pro-inflammatory effects and they have also been linked with chronic diseases including atherosclerotic and neurodegenerative processess. In the case of phytosterol oxidation products (POPs), more research is needed on toxic effects. Nevertheless, current knowledge suggests they may also cause cytotoxic and pro-apoptotic effects, although at higher concentrations than COPs. Recently, new beneficial biological activities of oxysterols are being investigated. Whereas COPs are associated with cholesterol homeostasis mediated by different mechanisms, the implication of POPs is not clear yet. Available literature on sources of oxysterols in the organism, metabolism, toxicity and potential beneficial effects of these compounds are reviewed in this paper.

Biological activities of 7-dehydrocholesterol-derived oxysterols: implications for Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is a metabolic and developmental disorder caused by mutations in the gene encoding the enzyme 7-dehydrocholesterol reductase (Dhcr7). This reductase catalyzes the last step in cholesterol biosynthesis, and levels of 7-dehydrocholesterol (7-DHC), the substrate for this enzyme, are elevated in SLOS patients as a result of this defect. Our group has previously shown that 7-DHC is extremely prone to free radical autoxidation, and we identified about a dozen different oxysterols formed from oxidation of 7-DHC. We report here that 7-DHC-derived oxysterols reduce cell viability in a dose- and time-dependent manner, some of the compounds showing activity at sub-micromolar concentrations. The reduction of cell survival is caused by a combination of reduced proliferation and induced differentiation of the Neuro2a cells. The complex 7-DHC oxysterol mixture added to control Neuro2a cells also triggers the gene expression changes that were previously identified in Dhcr7-deficient Neuro2a cells. Based on the identification of overlapping gene expression changes in Dhcr7-deficient and 7-DHC oxysterol-treated Neuro2a cells, we hypothesize that some of the pathophysiological findings in the mouse SLOS model and SLOS patients might be due to accumulated 7-DHC oxysterols.