Impact of De Novo Cholesterol Biosynthesis on the Initiation and Progression of Breast Cancer.

Cholesterol (CHOL) is a multifaceted lipid molecule. It is an essential structural component of cell membranes, where it cooperates in regulating the intracellular trafficking and signaling pathways. Additionally, it serves as a precursor for vital biomolecules, including steroid hormones, isoprenoids, vitamin D, and bile acids. Although CHOL is normally uptaken from the bloodstream, cells can synthesize it de novo in response to an increased requirement due to physiological tissue remodeling or abnormal proliferation, such as in cancer. Cumulating evidence indicated that increased CHOL biosynthesis is a common feature of breast cancer and is associated with the neoplastic transformation of normal mammary epithelial cells. After an overview of the multiple biological activities of CHOL and its derivatives, this review will address the impact of de novo CHOL production on the promotion of breast cancer with a focus on mammary stem cells. The review will also discuss the effect of de novo CHOL production on in situ and invasive carcinoma and its impact on the response to adjuvant treatment. Finally, the review will discuss the present and future therapeutic strategies to normalize CHOL biosynthesis.

Dietary palm oil enhances Sterol regulatory element-binding protein 2-mediated cholesterol biosynthesis through inducing endoplasmic reticulum stress in muscle of large yellow croaker (Larimichthys crocea).

Sterol regulatory element-binding protein 2 (SREBP2) is considered to be a major regulator to control cholesterol homoeostasis in mammals. However, the role of SREBP2 in teleost remains poorly understand. Here, we explored the molecular characterisation of SREBP2 and identified SREBP2 as a key modulator for 3-hydroxy-3-methylglutaryl-coenzyme A reductase and 7-dehydrocholesterol reductase, which were rate-limiting enzymes of cholesterol biosynthesis. Moreover, dietary palm oil in vivo or palmitic acid (PA) treatment in vitro elevated cholesterol content through triggering SREBP2-mediated cholesterol biosynthesis in large yellow croaker. Furthermore, our results also found that PA-induced activation of SREBP2 was dependent on the stimulating of endoplasmic reticulum stress (ERS) in croaker myocytes and inhibition of ERS by 4-Phenylbutyric acid alleviated PA-induced SREBP2 activation and cholesterol biosynthesis. In summary, our findings reveal a novel insight for understanding the role of SREBP2 in the regulation of cholesterol metabolism in fish and may deepen the link between dietary fatty acid and cholesterol biosynthesis.

Morusinol Extracted from Morus alba Inhibits Cell Proliferation and Induces Autophagy via FOXO3a Nuclear Accumulation-Mediated Cholesterol Biosynthesis Obstruction in Colorectal Cancer.

The incidence rate of colorectal cancer (CRC) has been increasing significantly in recent years, and it is urgent to develop novel drugs that have more effects for its treatment. It has been reported that many molecules extracted from the root bark of Morus alba L. (also known as Cortex Mori) have antitumor activities. In our study, we identified morusinol as a promising anticancer agent by selecting from 30 molecules extracted from Morus alba L. We found that morusinol treatment suppressed cell proliferation and promoted apoptosis of CRC cells in vitro. Besides this, we observed that morusinol induced cytoprotective autophagy. The GO analysis of differentially expressed genes from RNA-seq data showed that morusinol affected cholesterol metabolism. Then we found that key enzyme genes in the cholesterol biosynthesis pathway as well as the sterol regulatory element binding transcription factor 2 (SREBF2) were significantly downregulated. Furthermore, additional cholesterol treatment reversed the anti-CRC effect of morusinol. Interestingly, we also found that morusinol treatment could promote forkhead box O3 (FOXO3a) nuclear accumulation, which subsequently suppressed SREBF2 transcription. Then SREBF2-controlled cholesterol biosynthesis was blocked, resulting in the suppression of cell proliferation, promotion of apoptosis, and production of autophagy. The experiments in animal models also showed that morusinol significantly impeded tumor growth in mice models. Our results suggested that morusinol may be used as a candidate anticancer drug for the treatment of CRC.

Citri Reticulatae Pericarpium-Reynoutria japonica Houtt. herb pair suppresses breast cancer liver metastasis by targeting ECM1-mediated cholesterol biosynthesis pathway.

BACKGROUND: Liver metastasis is a frequent event in breast cancer that causes low survival rate and poor prognosis. Citri Reticulatae Pericarpium-Reynoutria japonica Houtt. (CR), a traditional Chinese herb pair, is used for the treatment of breast cancer liver metastasis or cholesterol gallstone disease in clinics. PURPOSE: This study attempted to investigate the potential therapeutic target and mechanism of CR herb pair on breast cancer liver metastasis. METHODS: The anti-metastatic and cholesterol-lowering activities of CR extract were evaluated in triple-negative breast cancer (TNBC) cell lines and an experimental liver metastasis model. The role of extracellular matrix protein 1 (ECM1) in the cholesterol biosynthesis pathway was determined by the knockdown and overexpression of ECM1 gene of TNBC cells. Changes in the gene and protein expression levels of ECM1 and the cholesterol biosynthesis pathway after CR treatment were detected in vitro and in vivo by real-time PCR and Western blot. RESULTS: The invasive and metastatic potentials and hypercholesterol levels of TNBC cells were positively associated with ECM1 expression. ECM1 knockdown reduced tumor cholesterol levels via downregulating cholesterol biosynthesis genes, including ACAT2, HMGCS1, HMGCR, MVK, and MVD, whereas ECM1 overexpression elicited the opposite effects. CR herb pair exerts the potential therapeutic effects on TNBC liver metastasis, which is partially mediated by disrupting ECM1-activated cholesterol biosynthesis process in TNBC cells. CONCLUSION: This study reveals that ECM1 is a novel target for the activation of cholesterol biosynthesis to promote TNBC liver metastasis occurrence. CR herb pair, an ECM1 inhibitor, maybe be considered to serve as an adjuvant therapeutic drug for liver metastasis in clinical practice.

An Update on Tamoxifen and the Chemo-Preventive Potential of Vitamin E in Breast Cancer Management.

Breast cancer (BC) is the most common female cancer in terms of incidence and mortality worldwide. Tamoxifen (Nolvadex) is a widely prescribed, oral anti-estrogen drug for the hormonal treatment of estrogen-receptor-positive BC, which represents 70% of all BC subtypes. This review assesses the current knowledge on the molecular pharmacology of tamoxifen in terms of its anticancer and chemo-preventive actions. Due to the importance of vitamin E compounds, which are widely taken as a supplementary dietary component, the review focuses only on the potential importance of vitamin E in BC chemo-prevention. The chemo-preventive and onco-protective effects of tamoxifen combined with the potential effects of vitamin E can alter the anticancer actions of tamoxifen. Therefore, methods involving an individually designed, nutritional intervention for patients with BC warrant further consideration. These data are of great importance for tamoxifen chemo-prevention strategies in future epidemiological studies.

Ursolic acid inhibits the cholesterol biosynthesis and alleviates high fat diet-induced hypercholesterolemia via irreversible inhibition of HMGCS1 in vivo.

BACKGROUND: In hypercholesteremia, the concentrations of total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) are enhanced in serum, which is strongly associated with an increased risk of developing atherosclerosis. Ursolic acid (UA), a pentacyclic terpenoid carboxylic acid, was found to alleviate hypercholesterolemia and hypercholesterolemia-induced cardiovascular disease. However, the specific targets and molecular mechanisms related to the effects of UA in reducing cholesterol have not been elucidated. PURPOSE: In this study, we aimed to illustrate the target of UA in the treatment of hypercholesterolemia and to reveal its underlying molecular mechanism. METHODS: Nontargeted metabolomics was conducted to analyze the metabolites and related pathways that UA affected in vivo. The main lipid metabolism targets of UA were analyzed by target fishing and fluorescence colocalization in mouse liver. Molecular docking, in-gel fluorescence scan and thermal shift were assessed to further investigate the binding site of the UA metabolite with HMGCS1. C57BL/6 mice were fed a high-fat diet (HFD) for 12 weeks to induce hypercholesteremia. Liver tissues were used to verify the cholesterol-lowering molecular mechanism of UA by targeted metabolomics, serum was used to detect biochemical indices, and the entire aorta was used to analyze the formation of atherosclerotic lesions. RESULTS: Our results showed that hydroxy­3-methylglutaryl coenzyme A synthetase 1 (HMGCS1) was the primary lipid metabolism target protein of UA. The UA metabolite epoxy-modified UA irreversibly bonds with the thiol of Cys-129 in HMGCS1, which inhibits the catalytic activity of HMGCS1 and reduces the generation of precursors in cholesterol biosynthesis in vivo. The contents of TC and LDL-C in serum and the formation of the atherosclerotic area in the entire aorta were markedly reduced with UA treatment in Diet-induced hypercholesteremia mice. CONCLUSION: UA inhibits the catalytic activity of HMGCS1, reduces the generation of downstream metabolites in the process of cholesterol biosynthesis and alleviates Diet-induced hypercholesteremia via irreversible binding with HMGCS1 in vivo. It is the first time to clarify the irreversible inhibition mechanism of UA against HMGCS1. This paper provides an increased understanding of UA, particularly regarding the molecular mechanism of the cholesterol-lowering effect, and demonstrates the potential of UA as a novel therapeutic for the treatment of hypercholesteremia.

Targeted inhibition of PPARα ameliorates CLA-induced hypercholesterolemia via hepatic cholesterol biosynthesis reprogramming.

BACKGROUND & AIMS: Disruption of lipid metabolism is largely linked to metabolic disorders, such as hypercholesterolemia (HCL) and liver steatosis. While cholesterol metabolic re-programmers can serve as targets for relevant interventions. Here we explored the dietary conjugated linoleic acids (CLA)-induced HCL in mice and the molecular regulation behind it. METHODS: A high dose of CLA supplementation in the diet was used to induce HCL in mice and was found to cause a hyper-activated cholesterol biosynthesis programme in the liver, leading to cholesterol metabolism dysregulation. The effects of a small-molecule drug targeting PPARα, i.e., GW6471 were studied in vivo in mice fed diets with CLA supplementation for 28 days, and in primary hepatocytes derived from HCL-mice in vitro. RESULTS: We demonstrate that CLA induced HCL and liver steatosis through multiple pathways. Among which was the PPARα-mediated cholesterogenesis. It was found to cooperate with SREBP2 via binding to Hmgcr and Dhcr7 (genes encoding key enzymes of the cholesterol biosynthetic pathway) and recruits the histone marks H3K27ac and H3K4me1 and cofactors. PPARα inhibition disrupts its physical association with SREBP2 by blocking cobinding of PPARα and SREBP2 to the genomic DNA response element. We showed that NR RORγ functions as an essential mediator that facilitates the interaction of PPARα and SREBP2 to modulate the cholesterol biosynthesis genes expression. CONCLUSIONS: Our study unravels that the small-molecule compound GW6471 exerts an attractive therapeutic effect for CLA-induced HCL, involving multiple pathways with the "PPARα-RORγ-SREBP2" being a potential complex player in this hepatic cholesterol biosynthesis programming.

Hibiscus syriacus L. cultivated in callus culture exerts cytotoxicity in colorectal cancer via Notch signaling-mediated cholesterol biosynthesis suppression.

BACKGROUND: In our previous study, Hibiscus syriacus leaf tissue was successfully cultivated in an optimized callus culture system, and subsequently extracted with 70% ethanol to prepare H. syriacus callus extract (HCE). The previous study suggested that the callus culture is useful method for obtaining the anti-inflammatory ingredients from H. syriacus. PURPOSE: In the present study, we aimed to investigate the effect of HCE on the colorectal cancer (CRC) and its underlying mechanism of action using HT-29 cells and thymus-deficient mice bearing HT-29 xenografts. METHODS: The cytotoxicity of HCE was investigated by MTT and colonies formation. The underling mechanism by which HCE regulates specific proteins in HT-29 cells was evaluated by the proteomic analysis. These putative proteins were validated using qRT-PCR and immunoblotting analyses. Subsequently, oral administration of HCE for 15 days further evaluating the anti-tumor activity by mRNA and protein expressions levels and tumor histopathology. RESULTS: Results of cell viability and colony formation assays revealed a significant cytotoxic effect of HCE at doses below 100 µg/ml against HT-29 cells, but not against normal cells. Through differential protein expression analysis, signaling pathways underlying anti-CRC activity were predicted in HCE-treated HT-29 cells: Notch signaling, cholesterol biosynthesis, and AMPK signaling pathways. qRT-PCR and immunoblotting analyses indicated that the cytotoxic effect of HCE against HT-29 cells might be associated with the suppression of Notch signaling, which positively contributes to cholesterol biosynthesis. To our knowledge, this can be presented as the first study to demonstrate the detailed relationship between Notch signaling and cholesterol-AMPK signaling. Our in vivo result further corroborated the in vitro finding that 100 and 200 mg/kg HCE for 15 days exerts its anti-cancer effect via Notch signaling-mediated suppression of cholesterol synthesis without systemic toxicity. CONCLUSION: Our findings can serve as a starting point for developing the novel anti-CRC agent using HCE, as a targeted medicine acting on regulating Notch signaling and cholesterol synthesis.

The Effects and Potential Mechanism of Oil Palm Phenolics in Cardiovascular Health: A Review on Current Evidence.

Cardiovascular disease (CVD) is globally known as the number one cause of death with hyperlipidemia as a strong risk factor for CVD. The initiation of drug treatment will be recommended if lifestyle modification fails. However, medicines currently used for improving cholesterol and low-density lipoprotein cholesterols (LDL-C) levels have been associated with various side effects. Thus, alternative treatment with fewer or no side effects needs to be explored. A potential agent, oil palm phenolics (OPP) recovered from the aqueous waste of oil palm milling process contains numerous water-soluble phenolic compounds. It has been postulated that OPP has shown cardioprotective effects via several mechanisms such as cholesterol biosynthesis pathway, antioxidant and anti-inflammatory properties. This review aims to summarize the current evidence explicating the actions of OPP in cardiovascular health and the mechanisms that maybe involved for the cardioprotective effects.

Exploring the effect of vitamin D3 supplementation on surrogate biomarkers of cholesterol absorption and endogenous synthesis in patients with type 2 diabetes-randomized controlled trial.

BACKGROUND: Inverse associations have been reported between serum 25-hydroxyvitamin D [25(OH)D] and circulating cholesterol concentrations in observational studies. Postulated mechanisms include reduced bioavailability of intestinal cholesterol and alterations in endogenous cholesterol synthesis. OBJECTIVE: To explore the effect of daily supplementation with 4000 IU/d vitamin D3 for 24 wk on surrogate biomarkers of cholesterol absorption (campesterol and ß-sitosterol) and endogenous synthesis (lathosterol and desmosterol). METHODS: Ancillary study of The Vitamin D for Established Type 2 Diabetes (DDM2) trial. Patients with established type 2 diabetes (N = 127, 25-75 y, BMI 23-42 kg/m2) were randomly assigned to receive either 4000 IU vitamin D3 or placebo daily for 24 wk. Of participants without changes in cholesterol-lowering medications (n = 114), plasma surrogate cholesterol absorption and endogenous synthesis biomarker concentrations were measured and merged with available measures of serum LDL cholesterol and HDL cholesterol concentrations. RESULTS: At week 24, vitamin D3 supplementation significantly increased 25(OH)D concentrations (+21.5 ± 13.4 ng/mL) but not insulin secretion rates (primary outcome of the parent study) as reported previously. In this ancillary study there was no significant effect of vitamin D3 supplementation on serum cholesterol profile or surrogate biomarkers of cholesterol absorption and endogenous synthesis. Compared with participants not treated with cholesterol-lowering medications, those who were treated exhibited a greater reduction in plasma campesterol concentrations in the vitamin D3 but not placebo group (P-interaction = 0.011). Analyzing the data on the basis of cholesterol absorption status (hypo- versus hyperabsorbers) or cholesterol synthesis status (hypo- versus hypersynthesizers) did not alter these results. CONCLUSIONS: Vitamin D3 supplementation for 24 wk had no significant effect on surrogate biomarkers of cholesterol absorption or endogenous synthesis, consistent with the lack of effect on serum cholesterol profile. Vitamin D3 supplementation resulted in greater reduction in campesterol concentrations in participants not using compared with those using cholesterol-lowering medications. Further studies are required.This trial was registered at clinicaltrials.gov as NCT01736865.

Acute exposure to oil induces age and species-specific transcriptional responses in embryo-larval estuarine fish.

Because oil spills frequently occur in coastal regions that serve as spawning habitat, characterizing the effects of oil in estuarine fish carries both economic and environmental importance. There is a breadth of research investigating the effects of crude oil on fish, however few studies have addressed how transcriptional responses to oil change throughout development or how these responses might be conserved across taxa. To investigate these effects, we performed RNA-seq and pathway analysis following oil exposure 1) in a single estuarine species (Cyprinodon variegatus) at three developmental time points (embryos, yolk-sack larvae, free-feeding larvae), and 2) in two ecologically similar species (C. variegatus and Fundulus grandis), immediately post-hatch (yolk-sack stage). Our results indicate that C. variegatus embryos mount a diminished transcriptional response to oil compared to later stages, and that few transcriptional responses are conserved throughout development. Pathway analysis of larval C. variegatus revealed dysregulation of similar biological processes at later larval stages, including alteration of cholesterol biosynthesis pathways, cardiac development processes, and immune functions. Our cross-species comparison showed that F. grandis exhibited a reduced transcriptional response compared to C. variegatus. Pathway analysis revealed that the two species shared similar immune and cardiac responses, however pathways related to cholesterol biosynthesis exhibited a divergent response as they were activated in C. variegatus but inhibited in F. grandis. Our results suggest that examination of larval stages may provide a more sensitive estimate of oil-impacts than examination of embryos, and challenge assumptions that ecologically comparable species respond to oil similarly.

Andrographolide is an Alternative Treatment to Overcome Resistance in ER-Positive Breast Cancer via Cholesterol Biosynthesis Pathway.

Oestrogen receptor (ER)-positive breast cancer is one of the common forms of breast cancer affecting women worldwide. ER-positive breast cancer patients are subjected to anti-oestrogen therapy such as selective oestrogen receptor modulator (SERM) and aromatase inhibitors (AIs). Recently, the emergence of resistance to anti-oestrogen treatment is under intensive focus. The different mechanisms postulated to explain the occurrence of resistance in ER-positive breast cancer treatment include the loss of ER function and the crosstalk between signalling pathways in cancer cells. Recent literature highlighted that the cholesterol biosynthesis pathway acts as a novel mechanism underlying resistance to oestrogen deprivation. The present study aimed to highlight the role of cholesterol biosynthesis in anti-oestrogen treatment resistance, putatively suggesting an alternative plant-based treatment using andrographolide from Andrographis paniculata. The hypolipidaemic effect of andrographolide can be utilised to prevent the resistance in the treatment of ER-positive breast cancer contributed by cholesterol biosynthesis.

Andrographolide is an Alternative Treatment to Overcome Resistance in ER-Positive Breast Cancer via Cholesterol Biosynthesis Pathway

@#Oestrogen receptor (ER)-positive breast cancer is one of the common forms of breast cancer affecting women worldwide. ER-positive breast cancer patients are subjected to antioestrogen therapy such as selective oestrogen receptor modulator (SERM) and aromatase inhibitors (AIs). Recently, the emergence of resistance to anti-oestrogen treatment is under intensive focus. The different mechanisms postulated to explain the occurrence of resistance in ER-positive breast cancer treatment include the loss of ER function and the crosstalk between signalling pathways in cancer cells. Recent literature highlighted that the cholesterol biosynthesis pathway acts as a novel mechanism underlying resistance to oestrogen deprivation. The present study aimed to highlight the role of cholesterol biosynthesis in anti-oestrogen treatment resistance, putatively suggesting an alternative plant-based treatment using andrographolide from Andrographis paniculata. The hypolipidaemic effect of andrographolide can be utilised to prevent the resistance in the treatment of ER-positive breast cancer contributed by cholesterol biosynthesis.

Identification and characterization of prescription drugs that change levels of 7-dehydrocholesterol and desmosterol.

Regulating blood cholesterol (Chol) levels by pharmacotherapy has successfully improved cardiovascular health. There is growing interest in the role of Chol precursors in the treatment of diseases. One sterol precursor, desmosterol (Des), is a potential pharmacological target for inflammatory and neurodegenerative disorders. However, elevating levels of the precursor 7-dehydrocholesterol (7-DHC) by inhibiting the enzyme 7-dehydrocholesterol reductase is linked to teratogenic outcomes. Thus, altering the sterol profile may either increase risk toward an adverse outcome or confer therapeutic benefit depending on the metabolite affected by the pharmacophore. In order to characterize any unknown activity of drugs on Chol biosynthesis, a chemical library of Food and Drug Administration-approved drugs was screened for the potential to modulate 7-DHC or Des levels in a neural cell line. Over 20% of the collection was shown to impact Chol biosynthesis, including 75 compounds that alter 7-DHC levels and 49 that modulate Des levels. Evidence is provided that three tyrosine kinase inhibitors, imatinib, ponatinib, and masitinib, elevate Des levels as well as other substrates of 24-dehydrocholesterol reductase, the enzyme responsible for converting Des to Chol. Additionally, the mechanism of action for ponatinib and masitinib was explored, demonstrating that protein levels are decreased as a result of treatment with these drugs.

Biological-Profiling-Based Systematic Analysis of Rhizoma Coptidis from Different Growing Regions and Its Anticholesterol Biosynthesis Activity on HepG2 Cells.

Rhizoma Coptidis is a widely cultivated traditional Chinese herb. Although the chemical profiles of Rhizoma Coptidis have been established previously, the biological profiling of Rhizoma Coptidis has not been conducted yet. In this study, we collected Rhizoma Coptidis varieties from four distinct growing regions and performed genome-wide biological response fingerprinting (BioReF) on HepG2 cells using a gene expression array. Similar biological pathways were affected by extracts of all four Rhizoma Coptidis varieties but not by their analogue, Mahoniae Caulis. Among these pathways, the terpenoid backbone biosynthesis pathway was highly enriched, and six genes in the mevalonate (MVA) pathway were all down-regulated. However, the expression, maturation, as well as the specific DNA binding capacity of their coordinate transcription factor, sterol response element binding protein 2 (SREBP2), was not affected by Rhizoma Coptidis extract (RCE) or its typical active alkaloid berberine. Cellular cholesterol content tests further verified the cholesterol-lowering function of RCE in vitro, which supplements evidence for the use of Rhizoma Coptidis in hyperlipidemia treatment. This is the first described example of evaluating the quality of Rhizoma Coptidis with BioReF and a good demonstration of using BioReF to uncover the mechanisms of herbs at a systematic level.

Cholesterol-lowering effects of dietary pomegranate extract and inulin in mice fed an obesogenic diet.

BACKGROUND: It has been demonstrated in animal studies that both polyphenol-rich pomegranate extract (PomX) and the polysaccharide inulin, ameliorate metabolic changes induced by a high-fat diet, but little is known about the specific mechanisms. OBJECTIVE: This study evaluated the effect of PomX (0.25%) and inulin (9%) alone or in combination on cholesterol and lipid metabolism in mice. METHODS: Male C57BL/6 J mice were fed high-fat/high-sucrose [HF/HS (32% energy from fat, 25% energy from sucrose)] diets supplemented with PomX (0.25%) and inulin (9%) alone or in combination for 4 weeks. At the end of intervention, serum and hepatic cholesterol, triglyceride levels, hepatic gene expression of key regulators of cholesterol and lipid metabolism as well as fecal cholesterol and bile acid excretion were determined. RESULTS: Dietary supplementation of the HF/HS diet with PomX and inulin decreased hepatic and serum total cholesterol. Supplementation with PomX and inulin together resulted in lower hepatic and serum total cholesterol compared to individual treatments. Compared to HF/HS control, PomX increased gene expression of Cyp7a1 and Cyp7b1, key regulators of bile acid synthesis pathways. Inulin decreased gene expression of key regulators of cholesterol de novo synthesis Srebf2 and Hmgcr and significantly increased fecal elimination of total bile acids and neutral sterols. Only PomX in combination with inulin reduced liver and lipid weight significantly compared to the HF/HS control group. PomX showed a trend to decrease liver triglyceride (TG) levels, while inulin or PomX-inulin combination had no effect on either serum or liver TG levels. CONCLUSION: Dietary PomX and inulin supplementation decreased hepatic and serum total cholesterol by different mechanisms and the combination leading to a significant enhancement of the cholesterol-lowering effect.

Statins increase hepatic cholesterol synthesis and stimulate fecal cholesterol elimination in mice.

Statins are competitive inhibitors of HMG-CoA reductase, the rate-limiting enzyme of cholesterol synthesis. Statins reduce plasma cholesterol levels, but whether this is actually caused by inhibition of de novo cholesterol synthesis has not been clearly established. Using three different statins, we investigated the effects on cholesterol metabolism in mice in detail. Surprisingly, direct measurement of whole body cholesterol synthesis revealed that cholesterol synthesis was robustly increased in statin-treated mice. Measurement of organ-specific cholesterol synthesis demonstrated that the liver is predominantly responsible for the increase in cholesterol synthesis. Excess synthesized cholesterol did not accumulate in the plasma, as plasma cholesterol decreased. However, statin treatment led to an increase in cholesterol removal via the feces. Interestingly, enhanced cholesterol excretion in response to rosuvastatin and lovastatin treatment was mainly mediated via biliary cholesterol secretion, whereas atorvastatin mainly stimulated cholesterol removal via the transintestinal cholesterol excretion pathway. Moreover, we show that plasma cholesterol precursor levels do not reflect cholesterol synthesis rates during statin treatment in mice. In conclusion, cholesterol synthesis is paradoxically increased upon statin treatment in mice. However, statins potently stimulate the excretion of cholesterol from the body, which sheds new light on possible mechanisms underlying the cholesterol-lowering effects of statins.

An Ester of ß-Hydroxybutyrate Regulates Cholesterol Biosynthesis in Rats and a Cholesterol Biomarker in Humans.

In response to carbohydrate deprivation or prolonged fasting the ketone bodies, ß-hydroxybutyrate (ßHB) and acetoacetate (AcAc), are produced from the incomplete ß-oxidation of fatty acids in the liver. Neither ßHB nor AcAc are well utilized for synthesis of sterols or fatty acids in human or rat liver. To study the effects of ketones on cholesterol homeostasis a novel ßHB ester (KE) ((R)-3-hydroxybutyl (R)-3-hydroxybutyrate) was synthesized and given orally to rats and humans as a partial dietary carbohydrate replacement. Rats maintained on a diet containing 30-energy % as KE with a concomitant reduction in carbohydrate had lower plasma cholesterol and mevalonate (-40 and -27 %, respectively) and in the liver had lower levels of the mevalonate precursors acetoacetyl-CoA and HMG-CoA (-33 and -54 %) compared to controls. Whole liver and membrane LDL-R as well as SREBP-2 protein levels were higher (+24, +67, and +91 %, respectively). When formulated into a beverage for human consumption subjects consuming a KE drink (30-energy %) had elevated plasma ßHB which correlated with decreased mevalonate, a liver cholesterol synthesis biomarker. Partial replacement of dietary carbohydrate with KE induced ketosis and altered cholesterol homeostasis in rats. In healthy individuals an elevated plasma ßHB correlated with lower plasma mevalonate.

Physiological feedback regulation of cholesterol biosynthesis: Role of translational control of hepatic HMG-CoA reductase and possible involvement of oxylanosterols.

Feedback regulation of cholesterol biosynthesis provides a mechanism to adapt to varying cholesterol input while maintaining rather constant serum and tissue cholesterol levels. The molecular mechanisms by which this occurs have been the subject of extensive investigation. This review focuses on the physiological mechanisms by which this regulation occurs. In animals that are sensitive to dietary cholesterol such as Golden Syrian hamsters, feedback regulation occurs mainly at the level of transcription of hepatic HMG-CoA reductase (3-hydroxy-3-methylglutaryl coenzyme A reductase). In animals like the Sprague Dawley rat that are resistant to the serum cholesterol raising action of dietary cholesterol, regulation occurs mainly at the level of translation efficiency of hepatic HMG-CoA reductase. Oxylanosterols were shown to effectively decrease translation of HMG-CoA reductase mRNA. Dietary cholesterol acts to significantly lower transcription of squalene epoxidase and lanosterol 14α demethylase favoring accumulation of the putative regulatory oxylanosterol-3ß-hydroxylanosterol-8-en-32-al. Thus, decreased transcription of enzymes occurring late in the cholesterol biosynthetic pathway appears to result in decreased translation of hepatic HMG-CoA reductase mRNA. These findings indicate that pronounced physiological feedback regulation of cholesterol biosynthesis in cholesterol resistant animals occurs at the level of translational efficiency without substantial reduction in hepatic HMG-CoA reductase transcription.