27-Hydroxycholesterol

27-Hydroxycholesterol is a selective estrogen receptor modulator and an agonist of the liver X receptor.

In Vitro:27-Hydroxycholesterol is an endogenous selective estrogen receptor modulator that displays significant partial agonist activity in a variety of cellular models of estrogen receptor action. It positively regulates both gene transcription and cell proliferation in cellular models of breast cancer[1]. 27-Hydroxycholesterol, through estrogen receptor activation, triggers deleterious effect in prostate cancer cell lines. 27-Hydroxycholesterol significantly increases cell proliferation of LNCaP and PC3 cells and this effect can be attenuated by estrogen receptor inhibitors[2]. 27-Hydroxycholesterol is an oxysterol produced from cholesterol by the monooxygenase CYP27A1, which regulates intracellular cholesterol homeostasis. 27-Hydroxycholesterol also acts as an endogenous selective estrogen receptor modulator capable of increasing breast cancer growth and metastasis. 27-Hydroxycholesterol levels can be modulated by statins or direct inhibition of CYP27A1, thereby attenuating its pro-tumorigenic activities[3]. 27-hydroxylation of cholesterol is an important pathway for LXR activation in response to cholesterol overload[4].

References:
[1]. DuSell CD, et al. 27-hydroxycholesterol is an endogenous selective estrogen receptor modulator. Mol Endocrinol. 2008 Jan;22(1):65-77. [2]. Raza S, et al. The cholesterol metabolite 27-hydroxycholesterol stimulates cell proliferation via ERβ in prostate cancer cells. Cancer Cell Int. 2017 May 11;17:52. [3]. Kimbung S, et al. Impact of 27-hydroxylase (CYP27A1) and 27-hydroxycholesterol in breast cancer. Endocr Relat Cancer. 2017 Jul;24(7):339-349. [4]. Fu X, et al. 27-hydroxycholesterol is an endogenous ligand for liver X receptor in cholesterol-loaded cells. J Biol Chem. 2001 Oct 19;276(42):38378-87.

Hematopoietic overexpression of Cyp27a1 reduces hepatic inflammation independently of 27-hydroxycholesterol levels in Ldlr(-/-) mice.[Pubmed:25281859]

J Hepatol. 2015 Feb;62(2):430-6.

BACKGROUND & AIMS: Non-alcoholic steatohepatitis (NASH) is characterized by hepatic lipid accumulation and inflammation. Currently, the underlying mechanisms, leading to hepatic inflammation, are still unknown. The breakdown of free cholesterol inside Kupffer cells (KCs) by the mitochondrial enzyme CYP27A1 produces 27-Hydroxycholesterol (27HC). We recently demonstrated that administration of 27HC to hyperlipidemic mice reduced hepatic inflammation. In line, hematopoietic deletion of Cyp27a1 resulted in increased hepatic inflammation. In the current manuscript, the effect of hematopoietic overexpression of Cyp27a1 on the development of NASH and cholesterol trafficking was investigated. We hypothesized that Cyp27a1 overexpression in KCs will lead to reduced hepatic inflammation. METHODS: Irradiated Ldlr(-/-) mice were transplanted (tp) with bone marrow from mice overexpressing Cyp27a1 (Cyp27a1(over)) and wild type (Wt) mice and fed either chow or a high-fat, high-cholesterol (HFC) diet for 3 months. Additionally, gene expression was assessed in bone marrow-derived macrophages (BMDM) from Cyp27a1(over) and Wt mice. RESULTS: In line with our hypothesis, hepatic inflammation in HFC-fed Cyp27a1(over)-tp mice was reduced and KCs were less foamy compared to Wt-tp mice. Remarkably, these changes occurred even though plasma and liver levels of 27HC did not differ between both groups. BMDM from Cyp27a1(over) mice revealed reduced inflammatory gene expression and increased expression of cholesterol transporters compared to Wt BMDM after lipopolysaccharide (LPS) stimulation. CONCLUSIONS: Our data suggest that overexpression of Cyp27a1 in KCs reduces hepatic inflammation independently of 27HC levels in plasma and liver, further pointing towards KCs as specific target for improving the therapy of NASH.

27-Hydroxycholesterol contributes to disruptive effects on learning and memory by modulating cholesterol metabolism in the rat brain.[Pubmed:25987203]

Neuroscience. 2015 Aug 6;300:163-73.

Cholesterol metabolism is important for neuronal function in the central nervous system (CNS). The oxysterol 27-Hydroxycholesterol (27-OHC) is a cholesterol metabolite that crosses the blood-brain barrier (BBB) and may be a useful substitutive marker for neurodegenerative diseases. However, the effects of 27-OHC on learning and memory and the underlying mechanisms are unclear. To determine this mechanism, we investigated learning and memory and cholesterol metabolism in rat brain following the injection of various doses of 27-OHC into the caudal vein. We found that 27-OHC increased cholesterol levels and upregulated the expression of liver X receptor-alpha (LXR-alpha) and adenosine triphosphate (ATP)-binding cassette transporter protein family member A1 (ABCA1). In addition, 27-OHC decreased the expression of 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CR) and low-density lipoprotein receptor (LDLR) in rat brain tissues. These findings suggest that 27-OHC may negatively modulate cognitive effects and cholesterol metabolism in the brain.

27-hydroxycholesterol mediates negative effects of dietary cholesterol on cognition in mice.[Pubmed:25453744]

Behav Brain Res. 2015 Feb 1;278:356-9.

In spite of the fact that cholesterol does not pass the blood-brain barrier, treatment of mice with dietary cholesterol causes significant effects on a number of genes in the brain and in addition a memory impairment. We have suggested that these effects are mediated by 27-Hydroxycholesterol, which is able to pass the blood-brain barrier. To test this hypothesis we utilized Cyp27-/- mice lacking 27-Hydroxycholesterol. The negative effect on memory observed after treatment of wildtype mice with dietary cholesterol was not observed in these mice. The cholesterol diet reduced the levels of the "memory protein" Arc (Activity Regulated Cytoskeleton associated protein) in the hippocampus of the wildtype mice but not in the hippocampus of the Cyp27-/- mice. The results are consistent with 27-Hydroxycholesterol as the mediator of the negative effects of cholesterol on cognition.

Relation between TLR4/NF-kappaB signaling pathway activation by 27-hydroxycholesterol and 4-hydroxynonenal, and atherosclerotic plaque instability.[Pubmed:25757594]

Aging Cell. 2015 Aug;14(4):569-81.

It is now thought that atherosclerosis, although due to increased plasma lipids, is mainly the consequence of a complicated inflammatory process, with immune responses at the different stages of plaque development. Increasing evidence points to a significant role of Toll-like receptor 4 (TLR4), a key player in innate immunity, in the pathogenesis of atherosclerosis. This study aimed to determine the effects on TLR4 activation of two reactive oxidized lipids carried by oxidized low-density lipoproteins, the oxysterol 27-Hydroxycholesterol (27-OH) and the aldehyde 4-hydroxynonenal (HNE), both of which accumulate in atherosclerotic plaques and play a key role in the pathogenesis of atherosclerosis. Secondarily, it examined their potential involvement in mediating inflammation and extracellular matrix degradation, the hallmarks of high-risk atherosclerotic unstable plaques. In human promonocytic U937 cells, both 27-OH and HNE were found to enhance cell release of IL-8, IL-1beta, and TNF-alpha and to upregulate matrix metalloproteinase-9 (MMP-9) via TLR4/NF-kappaB-dependent pathway; these actions may sustain the inflammatory response and matrix degradation that lead to atherosclerotic plaque instability and to their rupture. Using specific antibodies, it was also demonstrated that these inflammatory cytokines increase MMP-9 upregulation, thus enhancing the release of this matrix-degrading enzyme by macrophage cells and contributing to plaque instability. These innovative results suggest that, by accumulating in atherosclerotic plaques, the two oxidized lipids may contribute to plaque instability and rupture. They appear to do so by sustaining the release of inflammatory molecules and MMP-9 by inflammatory and immune cells, for example, macrophages, through activation of TLR4 and its NF-kappaB downstream signaling.

27-hydroxycholesterol is an endogenous selective estrogen receptor modulator.[Pubmed:17872378]

Mol Endocrinol. 2008 Jan;22(1):65-77.

Selective estrogen receptor (ER) modulators (SERMs) are ER ligands whose relative agonist/antagonist activities vary in a cell- and promoter-dependent manner. The molecular basis underlying this selectivity can be attributed to the ability of these ligands to induce distinct alterations in ER structure leading to differential recruitment of coactivators and corepressors. Whether SERM activity is restricted to synthetic ligands or whether molecules exist in vivo that function in an analogous manner remains unresolved. However, the recent observation that oxysterols bind ER and antagonize the actions of 17beta-estradiol (E2) on the vascular wall suggests that this class of ligands may possess SERM activity. We demonstrate here that 27-Hydroxycholesterol (27HC), the most prevalent oxysterol in circulation, functions as a SERM, the efficacy of which varies when assessed on different endpoints. Importantly, 27HC positively regulates both gene transcription and cell proliferation in cellular models of breast cancer. Using combinatorial peptide phage display, we have determined that 27HC induces a unique conformational change in both ERalpha and ERbeta, distinguishing it from E2 and other SERMs. Thus, as with other ER ligands, it appears that the unique pharmacological activity of 27HC relates to its ability to impact ER structure and modulate cofactor recruitment. Cumulatively, these data indicate that 27HC is an endogenous SERM with partial agonist activity in breast cancer cells and suggest that it may influence the pathology of breast cancer. Moreover, given the product-precursor relationship between 27HC and cholesterol, our findings have implications with respect to breast cancer risk in obese/hypercholesteremic individuals.

Differential effects of 24-hydroxycholesterol and 27-hydroxycholesterol on tyrosine hydroxylase and alpha-synuclein in human neuroblastoma SH-SY5Y cells.[Pubmed:19014385]

J Neurochem. 2008 Dec;107(6):1722-9.

Evidence suggests that environmental and dietary factors may contribute to the pathogenesis of Parkinson's disease (PD). High dietary intake of cholesterol is such a factor that has been shown to increase or decrease the risk of PD. However, because circulating cholesterol does not cross the blood-brain barrier, the mechanisms linking dietary cholesterol to the pathogenesis of PD remain to be understood. In contrast to cholesterol, the oxidized cholesterol metabolites (oxysterols), 24S-hydroxycholesterol (24-OHC) and 27-Hydroxycholesterol (27-OHC), can cross the blood-brain barrier and may place the brain at risk of degeneration. In this study, we incubated the human neuroblastoma SH-SY5Y cells for 24 h with 24-OHC, 27-OHC, or a mixture of 24-OHC plus 27-OHC, and have determined effects on tyrosine hydroxylase (the rate-limiting enzyme in dopamine synthesis) levels, alpha-synuclein levels, and apoptosis. We demonstrate that while 24-OHC increases the levels of tyrosine hydroxylase, 27-OHC increases levels of alpha-synuclein, and induces apoptosis. Our findings show for the first time that oxysterols trigger changes in levels of proteins that are associated with the pathogenesis of PD. As steady state levels of 24-OHC and 27-OHC are tightly regulated in the brain, disturbances in these levels may contribute to the pathogenesis of PD.

27-hydroxycholesterol is an endogenous ligand for liver X receptor in cholesterol-loaded cells.[Pubmed:11504730]

J Biol Chem. 2001 Oct 19;276(42):38378-87.

The nuclear receptors liver X receptor alpha (LXRalpha) (NR1H3) and LXRbeta (NR1H2) are important regulators of genes involved in lipid metabolism, including ABCA1, ABCG1, and sterol regulatory element-binding protein-1c (SREBP-1c). Although it has been demonstrated that oxysterols are LXR ligands, little is known about the identity of the physiological activators of these receptors. Here we confirm earlier studies demonstrating a dose-dependent induction of ABCA1 and ABCG1 in human monocyte-derived macrophages by cholesterol loading. In addition, we show that formation of 27-Hydroxycholesterol and cholestenoic acid, products of CYP27 action on cholesterol, is dependent on the dose of cholesterol used to load the cells. Other proposed LXR ligands, including 20(S)-hydroxycholesterol, 22(R)-hydroxycholesterol, and 24(S),25-epoxycholesterol, could not be detected under these conditions. A role for CYP27 in regulation of cholesterol-induced genes was demonstrated by the following findings. 1) Introduction of CYP27 into HEK-293 cells conferred an induction of ABCG1 and SREBP-1c; 2) upon cholesterol loading, CYP27-expressing cells induce these genes to a greater extent than in control cells; 3) in CYP27-deficient human skin fibroblasts, the induction of ABCA1 in response to cholesterol loading was ablated; and 4) in a coactivator association assay, 27-Hydroxycholesterol functionally activated LXR. We conclude that 27-hydroxylation of cholesterol is an important pathway for LXR activation in response to cholesterol overload.