Serum concentration of 27-hydroxycholesterol predicts the effects of high-cholesterol diet on plasma LDL cholesterol level

Tissue-Specific Oxysterols as Predictors of Antidepressant (Escitalopram) Treatment Response in Patients With Major Depressive Disorder

Background

There is growing evidence that disturbances in cholesterol metabolism may be involved in major depressive disorder (MDD). However, it is not known if cholesterol metabolites present in the brain and periphery can be used to diagnose and predict an MDD patient's response to antidepressant treatment.

Methods

A total of 176 subjects (85 patients with MDD and 91 healthy control subjects) were included in this study. The expression of peripheral and brain-specific oxysterols and related gene polymorphisms were investigated in all subjects. The severity of depression was measured using the 17-item Hamilton Depression Rating Scale, 16-item Quick Inventory of Depressive Symptoms-Self-Report, and Patient Health Questionnaire-9 for all patients with MDD before and after 12 weeks of antidepressant treatment.

Results

Patients with MDD expressed higher plasma levels of 24(S)-hydroxycholesterol (24OHC) (mainly secreted from the brain) compared with healthy control subjects, and the higher levels of 24OHC were associated with 24OHC synthetase (CYP46A1) gene polymorphisms. In patients with MDD, an improved response to the 12-week antidepressant treatment was associated with a reduction of both 24OHC and 27OHC (mainly secreted from the peripheral system) levels relative to baseline levels. Nonresponders exhibited increased levels of oxysterols at the end of treatment compared with baseline. The superior reduction in oxysterol levels correlated with better outcomes from the antidepressant treatment.

Conclusions

These data suggest a potential role for oxysterols as diagnostic and treatment response-related indicators for MDD.

Connecting the Dots Between Hypercholesterolemia and Alzheimer’s Disease: A Potential Mechanism Based on 27-Hydroxycholesterol

Alzheimer’s disease (AD), the most common cause of dementia, is a complex and multifactorial disease involving genetic and environmental factors, with hypercholesterolemia considered as one of the risk factors. Numerous epidemiological studies have reported a positive association between AD and serum cholesterol levels, and experimental studies also provide evidence that elevated cholesterol levels accelerate AD pathology. However, the underlying mechanism of hypercholesterolemia accelerating AD pathogenesis is not clear. Here, we review the metabolism of cholesterol in the brain and focus on the role of oxysterols, aiming to reveal the link between hypercholesterolemia and AD. 27-hydroxycholesterol (27-OHC) is the major peripheral oxysterol that flows into the brain, and it affects β-amyloid (Aβ) production and elimination as well as influencing other pathogenic mechanisms of AD. Although the potential link between hypercholesterolemia and AD is well established, cholesterol-lowering drugs show mixed results in improving cognitive function. Nevertheless, drugs that target cholesterol exocytosis and conversion show benefits in improving AD pathology. Herbs and natural compounds with cholesterol-lowering properties also have a potential role in ameliorating cognition. Collectively, hypercholesterolemia is a causative risk factor for AD, and 27-OHC is likely a potential mechanism for hypercholesterolemia to promote AD pathology. Drugs that regulate cholesterol metabolism are probably beneficial for AD, but more research is needed to unravel the mechanisms involved in 27-OHC, which may lead to new therapeutic strategies for AD.

Obesity, Type 2 Diabetes, and Cancer Risk

Obesity and type 2 diabetes have both been associated with increased cancer risk and are becoming increasingly prevalent. Metabolic abnormalities such as insulin resistance and dyslipidemia are associated with both obesity and type 2 diabetes and have been implicated in the obesity-cancer relationship. Multiple mechanisms have been proposed to link obesity and diabetes with cancer progression, including an increase in insulin/IGF-1 signaling, lipid and glucose uptake and metabolism, alterations in the profile of cytokines, chemokines, and adipokines, as well as changes in the adipose tissue directly adjacent to the cancer sites. This review aims to summarize and provide an update on the epidemiological and mechanistic evidence linking obesity and type 2 diabetes with cancer, focusing on the roles of insulin, lipids, and adipose tissue.

Interactions of Oxysterols with Atherosclerosis Biomarkers in Subjects with Moderate Hypercholesterolemia and Effects of a Nutraceutical Combination (Bifidobacterium longum BB536, Red Yeast Rice Extract) (Randomized, Double-Blind, Placebo-Controlled Study)

Background: Oxysterol relationship with cardiovascular (CV) risk factors is poorly explored, especially in moderately hypercholesterolaemic subjects. Moreover, the impact of nutraceuticals controlling hypercholesterolaemia on plasma levels of 24-, 25- and 27-hydroxycholesterol (24-OHC, 25-OHC, 27-OHC) is unknown. Methods: Subjects (n = 33; 18–70 years) with moderate hypercholesterolaemia (low-density lipoprotein cholesterol (LDL-C:): 130–200 mg/dL), in primary CV prevention as well as low CV risk were studied cross-sectionally. Moreover, they were evaluated after treatment with a nutraceutical combination (Bifidobacterium longum BB536, red yeast rice extract (10 mg/dose monacolin K)), following a double-blind, randomized, placebo-controlled design. We evaluated 24-OHC, 25-OHC and 27-OHC levels by gas chromatography/mass spectrometry analysis. Results: 24-OHC and 25-OHC were significantly correlated, 24-OHC was correlated with apoB. 27-OHC and 27-OHC/total cholesterol (TC) were higher in men (median 209 ng/mL and 77 ng/mg, respectively) vs. women (median 168 ng/mL and 56 ng/mg, respectively); 27-OHC/TC was significantly correlated with abdominal circumference, visceral fat and, negatively, with high-density lipoprotein cholesterol (HDL-C). Triglycerides were significantly correlated with 24-OHC, 25-OHC and 27-OHC and with 24-OHC/TC and 25-OHC/TC. After intervention, 27-OHC levels were significantly reduced by 10.4% in the nutraceutical group Levels of 24-OHC, 24-OHC/TC, 25-OHC, 25-OHC/TC and 27-OHC/TC were unchanged. Conclusions: In this study, conducted in moderate hypercholesterolemic subjects, we observed novel relationships between 24-OHC, 25-OHC and 27-OHC and CV risk biomarkers. In addition, no adverse changes of OHC levels upon nutraceutical treatment were found.

Esterification of 4β-hydroxycholesterol and other oxysterols in human plasma occurs independently of LCAT

The acyltransferase LCAT mediates FA esterification of plasma cholesterol. In vitro studies have shown that LCAT also FA-esterifies several oxysterols, but in vivo evidence is lacking. Here, we measured both free and FA-esterified forms of sterols in 206 healthy volunteers and 8 individuals with genetic LCAT deficiency, including familial LCAT deficiency (FLD) and fish-eye disease (FED). In the healthy volunteers, the mean values of the ester-to-total molar ratios of the following sterols varied: 4β-hydroxycholesterol (4βHC), 0.38; 5,6α-epoxycholesterol (5,6αEC), 0.46; 5,6β-epoxycholesterol (5,6βEC), 0.51; cholesterol, 0.70; cholestane-3β,5α,6β-triol (CT), 0.70; 7-ketocholesterol (7KC), 0.75; 24S-hydroxycholesterol (24SHC), 0.80; 25-hydroxycholesterol (25HC), 0.81; 27-hydroxycholesterol (27HC), 0.86; and 7α-hydroxycholesterol (7αHC), 0.89. In the individuals with LCAT deficiency, the plasma levels of the FA-esterified forms of cholesterol, 5,6αEC, 5,6βEC, CT, 7αHC, 7KC, 24SHC, 25HC, and 27HC, were significantly lower than those in the healthy volunteers. The individuals with FLD had significantly lower FA-esterified forms of 7αHC, 24SHC, and 27HC than those with FED. It is of note that, even in the three FLD individuals with negligible plasma cholesteryl ester, substantial amounts of the FA-esterified forms of 4βHC, 5,6αEC, 7αHC, 7KC, and 27HC were present. We conclude that LCAT has a major role in the FA esterification of many plasma oxysterols but contributes little to the FA esterification of 4βHC. Substantial FA esterification of 4βHC, 5,6αEC, 7αHC, 7KC, and 27HC is independent of LCAT.

Obesity and Cancer: 27-Hydroxycholesterol, the Missing Link

Obesity is currently affecting more than 40% of the Americans, and if it progresses with this rate, soon one out of two Americans will be obese. Obesity is an important risk factor for several disorders including cardiovascular disease, the first cause of death in the United States. Cancer follows as the second deadliest disease, and a link between obesity and cancer has been suggested. However, it is very hard to establish an exact connection between obesity and cancers due to the multifactorial nature of obesity. Hypercholesterolemia is a comorbidity of obesity and also linked to several cancers. Recently a cholesterol metabolite 27-hydroxycholesterol (27HC) was found to be an endogenous selective estrogen receptor modulator (SERM), which opened new doors toward several interesting studies on the role of this molecule in biological disorders. It is speculated that 27HC might be the missing link in the obesity and cancer chain. Here, we explored the effects of 27-hydroxycholesterol on obesity and cancers with a focus on the SERM capacity of 27HC.

Association between lifestyle, dietary, reproductive, and anthropometric factors and circulating 27-hydroxycholesterol in EPIC-Heidelberg

PURPOSE

Given that 27-hydroxycholesterol (27HC) is the first identified endogenous selective estrogen receptor modulator, the aim of this study was to investigate the extent to which dietary or lifestyle factors impact circulating 27HC concentrations in a large-scale setting.

METHODS

This cross-sectional analysis included 1,036 women aged 35-65 years who served as controls in the European Prospective Investigation into Cancer and Nutrition (EPIC)-Heidelberg breast cancer case-control study. Circulating 27HC was quantified in serum using liquid chromatography/tandem mass spectrometry. Generalized linear models were used to investigate the association between 27HC concentrations and dietary habits, and lifestyle, reproductive, and anthropometric factors.

RESULTS

Higher concentrations of 27HC were observed among postmenopausal relative to premenopausal women (geometric mean 200.5 vs. 188.4 nM, p = 0.03), whereas women reporting ever full-term pregnancy had lower concentrations of 27HC relative to never (191.4 vs. 198.6; p = 0.03). Significant trends were observed showing higher concentrations with relatively high levels of physical activity (p_trend = 0.03) and alcohol consumption (p_trend = 0.01), and women currently smoking at blood collection (p_trend < 0.01). Of the investigated dietary factors, starch (p_trend < 0.01) and thiamine (p_trend < 0.01) intakes were inversely associated with 27HC. Circulating lipid concentrations were positively associated with 27HC concentrations (all p_trend < 0.01). No significant associations were found between 27HC and factors including age at blood collection, body mass index, or use of hormone therapy or cholesterol-lowering medications.

CONCLUSION

27HC is of increasing interest for multiple chronic disease pathways. Despite significant associations found between circulating 27HC and dietary habits, reproductive factors, and modifiable lifestyle factors, circulating cholesterol, mostly low-density lipoprotein cholesterol, accounted for the majority of the variability in circulating 27HC.

Oxysterols and nuclear receptors

Oxysterols are derivatives of cholesterol and an important regulator of cholesterol metabolism, in part due to their role as ligands for nuclear receptors, such as the liver X receptors. Oxysterols are also known to be ligands for the RAR-related orphan receptors, involved in normal T cell differentiation. However, increasing evidence supports a role for oxysterols in the progression of several diseases. Here, we review recent developments in oxysterol research, highlighting the biological functions that oxysterols exert through their target nuclear receptors: the liver X receptors, estrogen receptors, RAR-related orphan receptors and the glucocorticoid receptor. We also bring the regulation of the immune system into the context of interaction between oxysterols and nuclear receptors, discussing the effect of such interaction on the pro-inflammatory function of macrophages and the development of T cells. Finally, we examine the impact that oxysterols have on various disease models, including cancer, Alzheimer's disease and atherosclerosis, stressing the role of nuclear receptors if previously identified. This review underscores the need to consider the multifaceted roles of oxysterols in terms of multiple receptor engagements and selective modulation of these receptors.

27-hydroxycholesterol decreases cell proliferation in colon cancer cell lines

Colorectal cancer (CRC) is the third most diagnosed cancer in the western world, affecting 1 out of approximately 22 people in their lifetime. Several epidemiological studies suggest a positive association between high plasma cholesterol levels and colorectal cancer. However, the molecular mechanisms by which cholesterol may alter the risk of colorectal cancer (CRC) are ill-defined as the cholesterol lowering drugs statins do not appear to decrease a patient's risk of developing colorectal cancer. Cholesterol is metabolized to active derivatives including cholesterol oxidization products (COP), known as oxysterols, which have been shown to alter cellular proliferation. These metabolites and not cholesterol per se, may therefore affect the risk of developing colorectal cancer. The cholesterol metabolite or the oxysterol 27-hydroxycholesterol (27-OHC) is the most abundant oxysterol in the plasma and has been shown to be involved in the pathogenesis of several cancers including breast and prostate cancer. However, the role of 27-OHC in colorectal cancer has not been investigated. We treated Caco2 and SW620, two well characterized colon cancer cells with low, physiological and high concentrations of 27-OHC, and found that 27-OHC reduces cellular proliferation in these cells. We also found that the effects of 27-OHC on cell proliferation are not due to cellular cytotoxicity or apoptotic cellular death. Additionally, 27-OHC-induced reduction in cell proliferation is independent of actions on its target nuclear receptors, liver-X-receptors (LXR) and estrogen receptors (ER) activation. Instead, our study demonstrates that 27-OHC significantly decreases AKT activation, a major protein kinase involved in the pathogenesis of cancer as it regulates cell cycle progression, protein synthesis, and cellular survival. Our data shows that treatment with 27-OHC substantially decreases the activation of AKT by reducing levels of its active form, p-AKT, in Caco2 cells but not SW620 cells. All-together, our results show for the first time that the cholesterol metabolite 27-OHC reduces cell proliferation in colorectal cancer cells.

Micro-environment and intracellular metabolism modulation of adipose tissue macrophage polarization in relation to chronic inflammatory diseases

The accumulation and pro-inflammatory polarization of immune cells, mainly macrophages, in adipose tissue (AT) are considered crucial factors for obesity-induced chronic inflammatory diseases. In this review, we highlighted the role of adipose tissue macrophage (ATM) polarization on AT function in the obese state and the effect of the micro-environment and intracellular metabolism on the dynamic switch of ATMs into their pro-inflammatory or anti-inflammatory phenotypes, which may have distinct influences on obesity-related chronic inflammatory diseases. Obesity-associated metabolic dysfunctions, including those of glucose, fatty acid, cholesterol, and other nutrient substrates such as vitamin D and iron in AT, promote the pro-inflammatory polarization of ATMs and AT inflammation via regulating the interaction between ATMs and adipocytes and intracellular metabolic pathways, including glycolysis, fatty acid oxidation, and reverse cholesterol transportation. Focusing on the regulation of ATM metabolism will provide a novel target for the treatment of obesity-related chronic inflammatory diseases, including insulin resistance, cardiovascular diseases, and cancers.

27-Hydroxycholesterol, an endogenous selective estrogen receptor modulator

Estrogen receptors (ERs) mediate the actions of the steroidal estrogens, and are important for the regulation of several physiological and pathophysiological processes, including reproduction, bone physiology, cardiovascular physiology and breast cancer. The unique pharmacology of the ERs allows for certain ligands, such as tamoxifen, to elicit tissue- and context-specific responses, ligands now referred to as selective estrogen receptor modulators (SERMs). Recently, the cholesterol metabolite 27-hydroxychoelsterol (27HC) has been defined as an endogenous SERM, with activities in atherosclerosis, osteoporosis, breast and prostate cancers, and neural degenerative diseases. Since 27HC concentrations closely mirror those of cholesterol, it is possible that 27HC mediates many of the biological effects of cholesterol. This paper provides an overview of ER pharmacology and summarizes the work to date implicating 27HC in various diseases. Wherever possible, we highlight clinical data in support of a role for 27HC in the diseases discussed.

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.

27-Hydroxycholesterol induces invasion and migration of breast cancer cells by increasing MMP9 and generating EMT through activation of STAT-3

Breast carcinoma plays a vital role in the reasons of global women's death. ER-related invasion and migration play an important part in the development and prognosis of breast cancer. Here, we found that 27-Hydroxycholesterol (27HC) could induce epithelial-mesenchymal transition (EMT) and increase the expression of the matrix metalloproteinase 9 (MMP9) at mRNA level and the active form. Meanwhile, interestingly, we found 27HC activated signal transducer and activator of transcription 3 (STAT-3) in ER positive cells except activation of ER signaling. Furthermore, inhibition of STAT-3 by siRNA attenuated the 27HC-induced improvement of MMP9 and decreased the invasion and migration ability in MCF7 and T47D cells. In addition, 27HC could also promote MMP9, vimentin and active STAT-3 in the ER negative cells MDA-MB-231. All these results not only raise a mechanism whereby 27HC enhances the invasion and metastasis, but also is helpful to realize 27HC as a potential endogenous detrimental factor in breast tumor patients.

Hydroxycholesterol Levels in the Serum and Cerebrospinal Fluid of Patients with Neuromyelitis Optica Revealed by LC-Ag+CIS/MS/MS and LC-ESI/MS/MS with Picolinic Derivatization: Increased Levels and Association with Disability during Acute Attack

Neuromyelitis optica (NMO) is an inflammatory demyelinating disease of the central nervous system (CNS). Hydroxycholesterols (OHCs), metabolites of CNS cholesterol, are involved in diverse cellular responses to inflammation and demyelination, and may also be involved in the pathogenesis of NMO. We aimed to develop a sensitive and reliable method for the quantitative analysis of three major OHCs (24S-, 25-, and 27-OHCs), and to evaluate their concentration in the cerebrospinal fluid (CSF) and serum of patients with NMO. The levels of the three OHCs in the serum and CSF were measured using liquid chromatography-silver ion coordination ionspray tandem mass spectrometry and liquid chromatography-electrospray ionization tandem mass spectrometry with picolinyl ester derivatization, respectively. The linear range was 5–250 ng/mL for 24S- and 27-OHC, and 0.5–25 ng/mL for 25-OHC in serum, and was 0.1–5 ng/mL for 24S- and 27-OHC, and 0.03–1 ng/mL for 25-OHC in CSF. Precision and accuracy were 0.5%–14.7% and 92.5%–109.7%, respectively, in serum, and were 0.8%–7.7% and 94.5%–119.2%, respectively, in CSF. Extraction recovery was 82.7%–90.7% in serum and 68.4%–105.0% in CSF. When analyzed in 26 NMO patients and 23 control patients, the 25-OHC (0.54 ± 0.96 ng/mL vs. 0.09 ± 0.04 ng/mL, p = 0.032) and 27-OHC (2.68 ± 3.18 ng/mL vs. 0.68 ± 0.25 ng/mL, p = 0.005) were increased in the CSF from NMO patients. When we measured the OHC_CSF index that controls the effects of blood–brain barrier disruption on the level of OHC in the CSF, the 27-OHC_CSF index was associated with disability (0.723; 95% confidence interval (CI)– 0.181, 0.620; p = 0.002), while the 24-OHC_CSF index (0.518; 95% CI– 1.070, 38.121; p = 0.040) and 25-OHC_CSF index (0.677; 95% CI– 4.313, 18.532; p = 0.004) were associated with the number of white blood cells in the CSF of NMO patients. Our results imply that OHCs in the CNS could play a role in the pathogenesis of NMO.

27-Hydroxycholesterol stimulates cell proliferation and resistance to docetaxel-induced apoptosis in prostate epithelial cells

Although the causes of prostate cancer (PCa) and benign prostatic hyperplasia (BPH) are not known, the role of oxidative stress, aging, and diet are suspected to increase the incidence of prostate complications. The cholesterol oxidation derivative (oxysterol) 27-hydroxycholesterol (27-OHC) is the most prevalent cholesterol metabolite in the blood. As aging, oxidative stress, and hypercholesterolemia are associated with increased risk of PCa and BPH, and because 27-OHC levels are also increased with aging, hypercholesterolemia, and oxidative stress, determining the role of 27-OHC in the progression of PCas and BPH is warranted. In this study, we determined the effect of 27-OHC in human prostate epithelial cells RWPE-1. We found that 27-OHC stimulates proliferation and increases androgen receptor (AR) transcriptional activity. 27-OHC also increased prostate-specific antigen expression and enhanced AR binding to the androgen response element compared to controls. Silencing AR expression with siRNA markedly reduced the 27-OHC-induced proliferation. Furthermore, 27-OHC blocked docetaxel-induced apoptosis. Altogether, our results suggest that 27-OHC may play an important role in PCa and BPH progression by promoting proliferation and suppressing apoptosis.

The Influence of an Obesogenic Diet on Oxysterol Metabolism in C57BL/6J Mice

Our current understanding of oxysterol metabolism during different disease states such as obesity and dyslipidemia is limited. Therefore, the aim of this study was to determine the effect of diet-induced obesity on the tissue distribution of various oxysterols and the mRNA expression of key enzymes involved in oxysterol metabolism. To induce obesity, male C57BL/6J mice were fed a high fat-cholesterol diet for 24 weeks. Following diet-induced obesity, plasma levels of 4β-hydroxycholesterol, 5,6α-epoxycholesterol, 5,6β-epoxycholesterol, 7α-hydroxycholesterol, 7β-hydroxycholesterol, and 27-hydroxycholesterol were significantly (P < 0.05) increased. In the liver and adipose tissue of the obese mice, 4β-hydroxycholesterol was significantly (P < 0.05) increased, whereas 27-hydroxycholesterol was increased only in the adipose tissue. No significant changes in either hepatic or adipose tissue mRNA expression were observed for oxysterol synthesizing enzymes 4β-hydroxylase, 27-hydroxylase, or 7α-hydroxylase. Hepatic mRNA expression of SULT2B1b, a key enzyme involved in oxysterol detoxification, was significantly (P < 0.05) elevated in the obese mice. Interestingly, the appearance of the large HDL₁ lipoprotein was observed with increased oxysterol synthesis during obesity. In diet-induced obese mice, dietary intake and endogenous enzymatic synthesis of oxysterols could not account for the increased oxysterol levels, suggesting that nonenzymatic cholesterol oxidation pathways may be responsible for the changes in oxysterol metabolism.

Increased serum liver X receptor ligand oxysterols in patients with non-alcoholic fatty liver disease

BACKGROUND

This study is a post-hoc analysis of a subset of patients who participated in our multi-institutional case-control study that evaluated the effects of pitavastatin in patients with non-alcoholic fatty liver disease (NAFLD) with hypercholesterolemia.

METHODS

Serum samples of fifteen patients with biopsy-proven NAFLD with dyslipidemia were investigated. Serum markers of lipid metabolism were quantified by liquid chromatography-mass spectrometry (LC-MS)/MS. These data were then compared with those of 36 sex- and age-matched healthy controls. In addition, changes in these markers produced by treatment with pitavastatin were evaluated.

RESULTS

Serum non-cholesterol sterols, reflecting intestinal cholesterol absorption, were significantly lower in the NAFLD patients compared to the controls, and the cholesterol synthesis marker, the ratio of lathosterol to cholesterol, was not significantly different between the two groups. Serum proportions of liver X receptor α (LXRα) ligand oxysterols (ratios to cholesterol) were significantly elevated in the NAFLD patients compared to the controls. The sum of oxysterols relative to cholesterol and the homeostasis model assessment as an index of insulin resistance (HOMA-IR) were significantly correlated. The marker representing cholesterol synthesis was significantly suppressed by pitavastatin treatment, from 3 months after initiation of the treatment, and the suppression remained significant during the observation period. The markers representing cholesterol absorption were unchanged at 3 months, but had significantly increased at 12 months. Serum oxysterol levels relative to cholesterol maintained high values and did not change significantly during the 12-month period of treatment.

CONCLUSIONS

We speculate that serum LXRα ligand oxysterol levels (relative to cholesterol) could be surrogate markers of insulin resistance, and that high oxysterol levels in the circulation may play an important role in the development of hepatic and peripheral insulin resistance followed by NAFLD.

27-Hydroxycholesterol: the first identified endogenous SERM

The cholesterol metabolite 27-hydroxycholesterol (27OHC) classically delivers sterols from peripheral tissues to the liver and is a substrate for bile acid synthesis. Recent studies have revealed that 27OHC also binds to and modifies the function of estrogen receptors ERα and ERβ. Experiments in mice lacking the enzyme which synthesizes 27OHC, CYP27A1, or the enzyme which catabolizes 27OHC, CYP7B1, have demonstrated that 27OHC adversely affects estrogen-related cardiovascular protection and bone mineralization. Work in breast cancer cells further indicates that 27OHC alters ER target gene expression to promote cell growth. Therefore, 27OHC is the first identified endogenous selective estrogen receptor modulator (SERM) and could have an important impact upon the cardiovascular system, bone biology, and cancer.

The endogenous selective estrogen receptor modulator 27-hydroxycholesterol is a negative regulator of bone homeostasis

Osteoporosis is an important clinical problem, affecting more than 50% of people over age 50 yr. Estrogen signaling is critical for maintaining proper bone density, and the identification of an endogenous selective estrogen receptor (ER) modulator, 27-hydroxycholesterol (27HC), suggests a mechanism by which nutritional/metabolic status can influence bone biology. With its levels directly correlated with cholesterol, a new possibility emerges wherein 27HC links estrogen and cholesterol signaling to bone homeostasis. In these studies, we found that increasing concentrations of 27HC, both by genetic and pharmacological means, led to decreased bone mineral density that was associated with decreased bone formation and increased bone resorption. Upon manipulation of endogenous estrogen levels, many of the responses to elevated 27HC were altered in such a way as to implicate ER as a likely mediator. In a model of postmenopausal bone loss, some pathologies associated with elevated 27HC were exacerbated by the absence of endogenous estrogens, suggesting that 27HC may act both in concert with and independently from classic ER signaling. These data provide evidence for interactions between estrogen signaling, cholesterol and metabolic disease, and osteoporosis. Patients with high cholesterol likely also have higher than average 27HC, perhaps putting them at a higher risk for bone loss and fracture. More studies are warranted to fully elucidate the mechanism of action of 27HC in bone and to identify ways to modulate this pathway therapeutically.

Proliferation of human mammary cancer cells exposed to 27-hydroxycholesterol

The aim of the present study was to identify the possible mechanisms by which certain estradiol receptor (ER)-positive mammary tumor cells remain resistant to treatment with anti-estrogens or inhibitors of local estradiol (E(2)) production. To this end, we compared the proliferative effects on mammary cancer cells of the novel selective ER modulator 27-hydroxycholesterol (27OHC) to those of E(2), and evaluated their inhibition by ICI 182,780 (ICI). Analysis of the effects on the cell cycle of 27OHC and E(2) in the absence or presence of ICI was conducted. In ER-positive mammary tumor cells, we detected the blocking of 27OHC proliferation-stimulatory activity by simvastatin, as well as the inhibition of E(2)-stimulated proliferation by an α-fetoprotein-derived cyclic nonapeptide. The effects reported herein may be extrapolated to infiltrating mammary cancer, where the activity of local macrophages may stimulate tumor growth. We suggest that increased breast cancer growth in obese patients may be related to increased 27OHC circulatory levels.